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4

THE VARIATION OF SPECIES

WITH ESPECIAL REFERENCE TO

THE INSECTA;

FOLLOWED BY

AN INQUIRY INTO

THE NATURE OF GENERA.

T. VERNON WOLLASTON, M.A., F.L.S.

** No compound of this earthly ball
Is like another, all in all.’’
TENNYSON.

LONDON:
JOHN VAN VOORST, PATERNOSTER ROW..
1856.

“J do not enter so far into the province of the logicians as to take notice of the dif-
ference there is between the analytic and synthetic methods of coming at truth, or
proving it ;—whether it is better to begin the disquisition from the subject, or from the
attribute. If by the use of proper media anything can be showed to he, or not to be,
I care not from what term the demonstration or argument takes its rise. Either way
propositions may beget their like, and more truth be brought into the world.’??—

Religion of Nature Delineated, p. 45 (A.D. 1722).

PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.

CHARLES DARWIN, Eso, M.A., V.P.R.S.,

Whose researches, in various parts of the world, have added

so much to our knowledge of Zoological geography,

this short Treatise

is dedicated.

PREFACE.

To make a dry subject entertaining, is impossible ;
but to render it, at any rate, readable, has been
my endeavour in the following pages. How far I
have succeeded in the experiment, it is not for me
to decide.

It having been suggested, by several of my
friends, that it might be desirable to bring together
into a small compass some of the evidence on
Insect variation (with reference to external disturb-
ing causes) which my researches in the Madeira
Islands have supplied me with, I have been en-
Couraged to do so: and I have added numerous
Conclusions from other data also, which have from

time to time fallen in my way,—so as to confer

on the volume a more practical interest, for the
general naturalist.

One of my main objects, however, has been to
call attention to the fact, that the Annulosa have
not been hitherto sufficiently considered, in the
great questions arising out of the distribution of
animals and plants; hoping that, by so doing,
some few of our British entomologists, who have
not looked into this branch of their science, may
be induced to enlist themselves in the cause of
Insect geography.

If such a result be brought about; or if I
be fortunate enough to open for discussion any
of the topics which have been touched upon, and
so lead to a more perfect solution of the problems
which I have attempted to explain, I shall con-
sider myself more than repaid.

10 Hereford Street, Park Lane, London,
May 10th, 1856.

Se : = ree

7
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ar ARETE aa

CONTENTS.

CHAPTER I.
Introductory Remarks

CHAPTER II.
Fact of Variation
As a matter of experience
As probable from analogy

CHAPTER III.
Causes of Variation

§ 1. Climatal causes generally (whether dependent
upon latitude or upon altitude)

§ 2. Temporary heat or cold, of an unusual degree ...

§ 3. Nature of the country, and of the soil

§ 4. Isolation; and exposure to a stormy atmosphere .

CHAPTER IV.

Organs and Characters of Variation

CHAPTER V.
Geological Reflections

CHAPTER VI.
The Generic Theory

Conclusion

CORRIGENDUM.

Page 90, for Pecteropus Maderensis read Pecteropus rostratus.

SPECIFIC VARIATION

INSECTA,

CHAPTER I.
INTRODUCTORY REMARKS. _

A very small amount of information gained by the
student in the field of Nature is sufficient to kindle the
desire to increase it. The more we know, the more we
are anxious to know; though the less we seem to know.
It is one of the distinctive privileges of the naturalist
that he has to labour in a mine which is inexhaustible:
the deeper he digs beneath the surface, the richer is the
vein for excavation, and the more interesting are the
facts which he brings successively to light. Dive he
ever so deep, Truth, “at the bottom of the well”. is
assuredly present, under some form or other, to reward
him still; nor will she even for once elude his grasp,
provided he be content to receive her as she is, instead
of endeavouring to mould her to his preconceived ideas
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of what she ought to be. In these times of patient re-
search, when the microscope is disclosing, day by day,
fresh wonders to our view, and new lines of speculation —
are springing out, as it were spontaneously, from the
regions of thought, it is remarkable that many of the
commoner questions relating to the members of the

external world around us have remained comparatively
unsolved ; nor indeed have some of them ever been dis-
cussed at all, except in a desultory manner and with
insufficient data to reason from. Foremost amongst

these, numerous problems affecting the distinction be-
tween “varieties” and “species” (as usually accepted)
of the animal kingdom stand pre-eminent,—especially
in the Annulose Orders, in which those distinctions are
less easy, à priori, to pronounce upon.

The descriptive naturalist, whose primary object it is

to register what he sees (apart from the obscurer phæ-
nomena which come within the province of the more

philosophical inquirer), can have scarcely failed to re-
mark the variation to which certain insects are at times
liable from the external agencies to which they have
been exposed: and yet, in spite of this, it is but too true
that even physiologists have frequently shunned the in-
vestigation of the circumstances on which such varia-
tions do manifestly in a great measure depend, as though
they were in no degree accountable for the changes in
question, and did not indeed so much as exist except in
theory. In the following pages I purpose, inter alia, to
throw out a few general hints ; first, on the fact of aber-

ration, as a mere matter of experience; and, secondly,
on some of the causes to which the physiologist would,
in many instances, endeavour to refer it.

The former of these considerations (namely, the fact
of specific instability as ordinarily noticed) nobody will

be inclined to dispute : and yet it is abundantly evident

that it cannot be taken into account, at any rate satis-
factorily, without involving the latter also,—it being
scarcely possible to attach the proper value to an effect
without first investigating its cause. The importance
of assigning its legitimate weight (and that only) to a
variety, is perhaps the most difficult task which the
natural historian has to accomplish ; since on it depends
the acknowledgment of the specific identity of one
object with another,—whilst, to draw the line of separa-
tion between varieties and species is indeed a Gordian
knot which generations have proved inadequate to untie.
Now it is not the object of this publication to attempt
to throw positively new light upon a subject which has
ever been one of the main stumbling-blocks in the lower
Sciences, and which is perhaps destined to be so to the
end; still less would I wish to imply that the causes of
variation are altogether overlooked in these days of
accurate inquiry,—when thousands are accumulating
data, in all parts of Europe, destined to be wielded by
the master’s hand whensoever the harvest-time shall
have arrived: but I do, nevertheless, believe that there
exists a growing tendency, especially in some portions of
the Continent, to regard every difference (if at all perma-
B 2

nent) as a specific one; and hence I gather the informa-
tion that areviewal of our first principles is occasionally
necessary, if we would not restrict (however gradual and -
imperceptibly) that legitimate freedom which Nature
has had chalked out for her to sport in, or strive to im-
pose laws of limitation in one department which we do
not admit to be coercive in another.

Perhaps, however, before entering on the subject-
matter of this treatise, my definition of the terms
“species” and “variety,’—so far at least as such is

, practicable,—will be expected of me. I may state, there-

. | fore, that I consider the former to involve that ideal re-
| lationship amongst all its members which the descent
\ from a common parent can alone convey: whilst the
‘latter should be restricted, unless I am mistaken, to
those various aberrations from their peculiar type which
are sufficiently constant and isolated in their general
character to appear, at first sight, to be distinct from it.

The first of these enunciations, it will be perceived,
takes for granted the acceptance of a dogma which I
am fully aware is open to much controversy and doubt,
—namely, that of “specific centres of creation.” With-
out, therefore, examining the evidences of that theory
which would be out of place in these pages (and which has
been so ably done already by the late Professor Edward
Forbes), I would merely suggest that the admission of it
is almost necessary, in order to convey to our minds any
definite notion of the word “species” at all: and that,
hence, whilst I would not wish to reject the hypothesis

as involving an absurdity (which I believe to be the
exact opposite of the truth), I would, in the present
State of our knowledge, desire rather to regard it as a
postulate, assumed to illustrate the doctrine of species,
than as a problem capable of satisfactory demonstration.

The second of the above definitions may likewise
require briefly commenting upon ; for I have frequently
heard it asserted that everything is to be regarded as a
“variety” which has wandered in the smallest degree

from its normal state. Now this I contend is essentially ~_

an error; for a “variety,” to be technically such, must
have in it the primd- 1-facie elements of stability, —and to
an extent moreover that, without the intermediate Slee
(which, although rarer than the variety itself, must. — g
nevertheless exist) to connect it with its parent stock,
its condition is such that it might be registered as speci- |
fically distinct therefrom. Thus, to take an example for’
illustration, there are many darkly coloured insects
which, as every entomologist knows, vary, by slow and
regular gradations, into a pallid hue, sometimes into
almost white. It also most frequently happens, in such
instances, that the extreme aberration is of more common
occurrence than the intermediate ones. Here then is a
case in point: there is but a single variety involved,
namely a pale one,—the gradually progressive shades |
which imperceptibly affiliate it with its type not being (
regarded in themselves as “varieties” at all. If this |
indeed were not so, then would our position be far from
pleasant, since we should be compelled to record, as a

variety, every separate degree of colour which could
possibly be found between the outer limits,—seeing that

(increasing, as they did, in an even ratio) no one could
be tabulated in preference to another.

This however is an example in which the rate of altera-
tion (so far as colour is concerned) is egual; and one
therefore in which the extreme end of the series can be
alone singled out as the aberration to be specially noticed.
It sometimes occurs that, between the two extremes,
there are several nuclei, or centres of radiation, to which
the name of varieties may be legitimately applied,—in-
asmuch as they may possess a series of characters which
do not, all, in combination, progress evenly ; and which
consequently stand out as it were, to a certain extent
isolated, from the remainder.

As a corollary arising out of these remarks, it would
seem to follow that even small differences should be re-
garded as specific ones so long as the intermediate links
have not been detected which may enable us to refer
them to their nearest types. In a general sense, I
believe that it would be proper to do so: nevertheless
there are instances, the results, for example, of isolation,
in which abrupt modifications may be à priori looked
for; and in which our judgment must be regulated by
our knowledge of the local circumstances which may be
reasonably presumed to have had some influence in pro-
ducing them. ‘The consideration of these, however, and
other kindred questions, must be deferred to a subse-
quent chapter of this work.

CHAPTER II.
FACT OF VARIATION,

Ir is scarcely possible to survey the members of the
external world around us without being struck with the
instability with which everything is impressed. The
very shadows, as they pass, leave a moral lesson behind
them on the mountain-slope, which the student of
Nature would do well to contemplate. Whatever be.
our preconceived ideas of the “immutability of the uni-
verse,” from first to last the same truth is re-echoed to
our mind,—that here all is change. Organic and in-
organic matter are alike subjected to renovation and
decay ; and, dependent on that general law, variability

within specific limits would seem to be an almost neces-

sary consequence. In the animal and vegetable king-
doms, this principle of fluctuation is peculiarly apparent ;
and not more surely do the winds of heaven ruffle the
forests over which they rage, than does the ebb and flow
which is perpetually gomg on amongst created things
mar their boasted constancy.

The fact of aberration, to which we would briefly
allude in this chapter, requires but little comment; it is
patent à priori. As a matter of experience, every ob-
Server who has spent a week in the field of Nature

knows it to exist. However difficult it may be, in some
instances, to distinguish aright between Species and
varieties, as rigidly defined, there is an instinct within
us which often recognizes the latter, even at first sight,
as unmistakeably such: and in these cases, a well-edu-
cated eye, although of course occasionally deceived, will
not often be found to err.
z In the vegetable world this proneness to variation is
self-evident ; and botanists innumerable, who have in-
vestigated the causes on which the modifications of cer-
tain plants have been presumed to depend, have not
been behindhand in acknowledging it. Soil, climate,
altitude, and a combination of other circumstances and
conditions, have been successively taken into account,
and to each an amount of disturbing influence (more or
less, as the case may be) has been conceded. “The
more powerful agents,” writes Professor Henfrey, “ en-
force their general laws, but every little local action
asserts its qualifying voice; and we see that all these
irregularities and uncertainties (as we in our ignorance
call them, and complain of) are necessary and important
parts of a great whole, —are but isolated features of a
comprehensive plan, in accordance with which all work
in concert to bring about that change absolutely indis-
pensable to the existence of animal and vegetable life
upon the earth’s surface, and that variety of conditions
by which is ensured a fitting abode for each kind of its
multifarious and diversified inhabitants.”

Whilst exploring the barren moor, or bleak upland

heights, the botanist would as assuredly look for a
change in the outward configuration of certain species,
which colonize equally the rich meadows and teeming
ravines, as a geographical difference is à priori antici-
pated between the hard, sturdy mountaineer and the
more enervated denizen of the plain. A daisy, gathered
on the cultivated lawn, has usually attained a greater
degree of perfection and luxuriance than its companion
from the sterile heath; and the bramble which chokes
up the ditches of the sheltered hedgerow, wears a very
different aspect from its stunted brother of the hills.
Nor is this dependency on external circumstances less
apparent in the animal kingdom also,—the domesticated
races of which every agriculturist is aware are capable
of modification, artificially, to an almost unlimited ex-
tent; and which exhibit, when even in a state of nature,
nearly as great a variety, from purely natural causes, as
they have been proved to do when subjected to the laws
and routine of agrarian science. Take the sheep, for
example, of Dartmoor or Wales, and compare them with
those from the wolds of Lincolnshire and the downs of
Kent; or contrast. the Hereford oxen with those of the
midland counties, or of the Caledonian breed, still extant
in Cadzow Forest, and it will require but little argument
to convince us how important is the operation of local
circumstances in regulating the outward contour of these
higher creatures. If therefore this general obedience to
influences from without be self-evident in the vegetable
world, and equally traceable amongst the Mammalia,

why, we may ask, are the lower members of the animal
creation to be denied analogous effects from the same
causes ?

We are often told that the Annulosa present so many
anomalies in their organization, that we cannot apply
the argument of analogy, when reasoning on their struc-
ture and attributes; and that we must consequently be
content to leave it an open question, as to whether or
not they possess anything in common with the Verte-
brata, or can be presumed to be acted upon, by external
agencies, in at all a similar manner. Now, whilst there
is clearly some truth in this assertion (especially as
regards the senses of insects, which must ever remain a
subject of obscurity), I contend that to accept it in all
its fullness would be in the highest degree unphiloso-
phical; whilst, to endorse it to the extent which even
its partial advocates do insist upon, would at once
involve us in a host of difficulties (affecting other de-
partments of natural science), the very existence of
which they have themselves tacitly repudiated.

_ “Creation,” says one of our most intelligent writers
of modern times, “is full of analogies, pointing to one
general originator, and linking all sentient things into
one great family of related fellow-creatures :”—and
there is an amount of sagacity in the remark which it
would be wise for us to digest. Throughout the whole
of animated nature, it is impossible not to perceive that
certain circumstances do, in the main, produce certain
results. They may often fail to produce them, and the

results themselves may frequently be modified (or, ap-
parently, even reversed), from counter influences of
divers kinds. This touches not, however, the existence
of the law; and the effect is not the less specifically
dependent on its own peculiar cause, because those
“counter influences”? prevail, —and because different
effects may chance, therefore, to be occasionally brought

about by causes which may possibly seem to be identical.
We should, rather, bear in mind that the agents which
operate in moulding the outward contour of organic

beings are various, and capable ¿nter se of permutations
innumerable; so that it is only on a broad scale that
parallel results can be looked for in creatures severally
exposed to the action of elements, which are liable to be
differently compounded from what may primá facie
appear to be the case: and that, consequently, where
opposite phænomena are displayed under circumstances
seemingly coincident, our first object should be (not to
regard the phænomena as indicative, that no constant
result can be anticipated from causes which are similar,
but), to inquire whether the circumstances in question
are really coincident or not,—seeing that some counter-
acting stimulus may have been, here or there, unex-
pectedly at work, which shall enable us, so soon as it is
detected, to account for the discrepancy.

It is by this process alone that we can hope to make
real use of analogy, without abusing it: for whilst there
is danger, on the one hand, of needlessly rejecting the
argument which it suggests to us, through opposite

effects being observed (amongst the members of the
organic world) from conditions which we assume to be
co-ordinate, but which in fact are not so ; we may, on
the other, run a similar risk (and thus fail to discern a
corresponding modus operandi in the maturation of like
results), from a mere à priori belief that the lower
animals cannot be acted upon, by external influences, in
a manner at all equivalent to that which is self-evident
in the higher ones.

“To make a perfect observer in any department of
science,” writes Sir John Herschel, “an extensive ac-
quaintance is requisite, not only with the particular
science to which his observations relate, but with every
branch of knowledge which may enable him to appre-
ciate and neutralize the effect of extraneous disturbing
causes. Thus furnished, he will be prepared to seize on
any of those minute indications which often connect
phenomena which seem quite remote from each other.
He will have his eyes as it were opened, that they may
be struck at once with any occurrence which, according
to received theories, ought not to happen; for these are
the facts which serve as clews to new discoveries*.”

There can be no doubt that amongst a large proportion
of our naturalists, differences, as such, are too exclusively
studied. Essential as their investigation is (for we could
not progress a step without some presumptive notion as
to the specific identity, or not, of the objects about which

* Preliminary Discourse on the Study of Natural Philosophy
(London, 1830), p. 132.

we have to treat), we should not forget that there are
other questions, likewise, which ought to occupy our
attention in, at any rate, an almost equal degree,—as
being of eminent significance in guiding us to a correct
interpretation of the phenomena with which we have to
deal. Such are, more especially, similitudes and ana-
logies, in their widest sense,—which are too often
neglected, even by those who admit the necessity of
recognizing them where they may be shown to exist.
Lord Bacon, in referring to a similar tendency amongst
a certain section of the naturalists of his day, remarks

(though perhaps his love of analogies may have led him

to somewhat overrate their importance): “Up to this
time the industry of men has been great, and very curi-
ous in marking the variety of things, and explaining the
accurate differences of animals, herbs, and fossils,—the
chief part of which are the mere sport of Nature, rather
than serious and of use toward the sciences. Such
things tend to our enjoyment, and sometimes to even
practical use; but little or nothing towards an insight
into Nature. And so our labour is to be turned to in-
quiry into, and notice of, similitudes and analogies, both
in the whole and in the parts of things: for these are
they which unite Nature, and begin to establish
Sciences*.”’

* « Magna enim hucusque atque adeo curiosa fuit hominum in-
dustria, in notanda rerum varietate, atque expliċandis accuratis
animalium, herbarum, et fossilium differentiis; quarum pleræque
magis sunt lusus naturæ, quam seriæ alicujus utilitatis versus

I believe that, if analogies were more carefully studied
in the lower departments of the animal kingdom, we
should be less inclined to deny some sort of uniformity
to the action of elements and conditions which, by a
law of Nature, must at times operate equally upon the
various and dissimilar members of the organic creation.
Amongst the Insecta, where the individuals exist in such
multitudes that accuracy in generalizations concerning
them, becomes, as it were, peculiarly within our reach,
this doctrine cannot be too rigidly insisted upon ; and it
is not difficult to foresee that, should the principle of
external disturbing influences ever be admitted by ento-
mologists to the extent which it has been accepted by
the students of the Vertebrata, our so-called “ species”
will have to submit to a process of elimination and
inquiry, which at present would be well nigh incre-

dible. The time for such a step is yet far off: perhaps

indeed, considering the innovations of nomenclature
which it would necessitate, it will never arrive at all;
yet the fact remains the same, that, if analogy with
creatures of a more perfect development be not altogether
disallowed us, during our researches into the insect
tribes, or ¿f similar causes may be presumed to have
somewhat similar effects in opposite sections of the
scientias. Faciunt certe hujusmodi res ad delectationem, atque
etiam quandoque ad praxin; verum ad introspiciendam naturam
parum aut nihil. Itaque convertenda plane est opera ad inquiren-
das et notandas rerum similitudines et analoga, tam in integralibus,

quam partibus: illæ enim sunt, quæ naturam uniunt, et constituere
scientias incipiunt.” —Novum Organum, lib. ii. 27.

animate world, an enlargement of our prescribed limits,
for specific variation, ought in reality to follow (sooner
or later) as an inevitable consequence.

In whichever light, therefore, insect aberration is
viewed. by us,—whether as a matter of experience (which,
being self-evident, will satisfy the practical observer), or
as probable from analogy (which will hardly be denied,
at any rate to a certain extent, by even the most theo-
retical), — we affirm that it does, ipso facto, ewist.
“There is no similitude in Nature that owneth not also
to a difference ;”’ let this be constantly borne in mind,
for it is a truism almost beyond controversy, and one

which, to a reflective mind, will scarcely admit of a
doubt. l
It will be perceived, from the above remarks, that I

draw a distinction between insects which simply vary
(that is to say, which aberr from their normal state),
and those which afford (in the sense as enunciated in
the last chapter) one or more actual “ varieties,” —
technically so called: and it will be further gathered,
that, whilst I regard the former as universally to be met
with, the latter are, on the contrary, of only occasional
occurrence. That positive and well-defined varieties, or
races, should be confined to certain species, is not re-
markable ; but that every individual insect should differ,
however slightly, from its nearest relation and ally, may
perhaps require some few words of explanation, even to
a naturalist. It is not essential however to our present
Subject (which is merely a plea for specific variation

generally, as commonly understood) that any such
dogma should be propounded; nevertheless, since all

analogy teaches us to anticipate it, and observation tends
more and more, as our knowledge advances, to corrobo-
rate the fact, I shall be pardoned for venturing a passing
thought upon a question even thus difficult of demon-
stration.

Perhaps we are too prone to regard those specific
characters, which are so subtle that they cannot be
grasped by our clumsy faculties except in their broadest

and plamest features, as incapable of fluctuation. Yet a
| practised eye can detect discrepancies innumerable in
specimens which appear absolutely alike to one that is
uneducated; whilst a third person, better qualified stall,
will trace out other and more delicate distinctions, with

i
H

even greater precision. And thus it is that we rise, step
by step, even amongst the humbler representatives of
the animal kingdom, to the comprehension of that great
truth which is so conspicuous in the nobler ones, and
which we have already summoned to our aid, that “there
is no similitude in Nature which owneth not also to a

difference.” Let us not forget that the sphere of our

senses is limited; and that, although tuition will do
much to enlarge their capacity for perception, we are at
the best but a dim-sighted race: hence, we should be
careful to avoid conclusions which are not warranted by

analogy, and which our understanding, as it becomes
gradually brighter, no less assuredly condemns. True
it is, that we may not be able, as in the higher animals,

to appreciate the differences between individuals without
a rigid inspection, and that sometimes we may fail to do
so even when the objects are critically examined ; yet
the fact that new peculiarities do unquestionably open
out upon us, as we become more and more trained for
the recognition of them, ought to warn us that others
may exist likewise, despite our primá-facie conclusions ;
whilst analogy with what we know to be the case in
_ other departments of the organic world should suggest,
unless indeed there is presumptive evidence to the con-
trary, that they in all probability do. i

The Alpine range, when seen from afar, appears a
monotonous mass of a dull uniform hue; and nothing,
of all the wondrous details which it includes, can be
distinguished, except perchance the outline of its jagged
peaks projected in faint relief against the distant sky.
One by one, however, as we approach it, inequalities
present themselves ; the surface which lately seemed so
uniform and grey that it could be compared only to a
cloud, is found to be cleft by ravines; and valleys, in all
their magnificence and breadth, expand slowly to our
view. Yet, marvellous as is the change, this is not all :
wood and water, without which the landscape would be
barren, are in turn revealed; whilst the play of light
and shade upon the mountain-slopes proclaims at length
that the picture is well nigh complete. Still more to be
disclosed does in reality remain; and we must advance
nearer yet if we would either fully realise the whole, or
enter into the surprising minutiz of each of its com-

ponent parts. And so it is with the objects which we
have been just discussing. When contemplated in a
mass, and by an uneducated eye, hosts of them may

appear to be identical; but as our vision becomes clearer

and more acute, differences, formerly inappreciable, are
gradually made manifest,—until at last we can detect
modifications innumerable, throughout the entire length
of the living panorama; and are enabled to endorse the
belief (repugnant à priori though it be), that individual
variations, even to the extent which I have ventured to
suggest, are not incompatible with specific similitudes.

CHAPTER III.
CAUSES OF VARIATION.

“Tr is not impossible,” says a writer of the last century,
“that such laws of Nature, and such a series of causes
and effects, may have been originally designed, that not
only general provisions may have been made for the
several species of beings, but that even particular cases
(at least many of them) may have been provided for
Without innovations in the course of Nature*.’ And
let us not suppose that this is a mere wanton specula-
tion, unsupported by evidence (if not actually circum-
stantial, at least) strongly presumptive ; since the further
we penetrate into the ramifications of the organic world,
the less are we inclined to ignore the operation of those

various modifying influences which our understanding

tells us do everywhere exist.

To investigate the causes of things, and to endeavour
to trace out by slow, inductive processes those second-
ary agents, by the assistance of which a large propor-
tion of the phenomena around us are gradually matured,
is no insignificant task; yet how much animadversion
from without have the students in such fields of research
frequently to endure! A fact many times repeated, and
which comes within our daily experience, is too often

* Religion of Nature Delineated, p. 103.

looked upon as a matter of course, and as therefore
beneath the notice of an intelligent mind: yet the man
who regards ¿ruth as valuable, for its own sake, under
whatever aspect it may come, and who can rise to the
appreciation of results, whether they be of rare or con-
stant occurrence, will have learnt to pronounce nothing
as unimportant which may supply a single link in that
chain of knowledge which would be broken and im-
perfect without it. A spirit of inquiry, however, is
becoming, year by year, more evident; and we may con-
fidently anticipate the period when such reproaches will
have for ever died away. Natural history, in all its
branches, will then advance more rapidly than hereto-
fore, and each separate labourer, in his own peculiar
province, will breathe a more genial atmosphere ; whilst
observation and reason, mutually dependent on each
other, will work in concert more effectually. “ Reason
without observation,” writes the author above quoted,
“wants matter to act upon: and observations are neither
to be justly made by ourselves, nor to be rightly chosen
out of those collected by others, without the assistance
of reason. Both together may support opinion and
practice, in the absence of knowledge and certainty.”
In the last chapter we offered a few passing remarks
on insect-aberration generally, whether regarded as a
universal fact (which, however, even supposing such to
be true, it is not the object of the present treatise to
substantiate), or as an occasional one,—that is to say,
as existing at all times to that extent (as an hereditary

principle), that it is liable to manifest itself, or not,
according as external agencies may favour or oppose its
occurrence. In the latter case, which alone I propose
to consider, this inherent tendency may be displayed,
either through the expression of “ varieties” well de-

fined, or by a mere proneness to wander, irregularly and

at large, from an assumed diagnostic type. In the fol-
lowing pages, the former of these resultant conditions
(namely, that in which “ varieties,” technically so called,
though more or less isolated in their character, are appa-
rent) will be especially discussed; since my principal
desire is, to point out the influence of local disturbing
causes in regulating, to a greater or less extent, though
of course within certain specific limits, the outward
contour of the insect tribes,—and it requires no argu-
ment to prove that, where those local elements (whatso-
ever they may be) prevail, the same effects will, for the
most part (in the same species), be produced; and that,
therefore, modifications which are characteristic of coun-
tries and regions far removed from each other have an
à priori claim for stability, above those which circum-
stances less important than geographical ones, and
which are consequently more fluctuating in their com-
binations, may from time to time (as it were, accident-
ally) shape out. Having then examined our premises,
and prepared ourselves, with an unbiassed mind, for the
reception of phenomena which should be constant (and
in some instances, also, conspicuous) in proportion as
the conditions which unite in bringing them about are

significant ; let us advert to a few of the more prominent
cases in which our instinct would seem to warrant the
belief that aberrations are to be usually anticipated.
And since it will hardly be denied that, like the repre-
sentatives of other departments of the animate world,
insects may, in their outward configuration and deve-
lopment, be in some measure under the control of the
external influences to which they are immediately ex-
posed, we will take a rapid glance at a few of the circum-
stances and conditions which are known to have more or
less of a qualifying effect on the members of large and
opposite sections of the organic creation; and then see
how far we are enabled, by means of facts, to trace out
results for the Insecta, corresponding to those which are
admitted to obtain in the other groups. And, since the
existence of analogous results infers, to a certain extent,
the similarity of the agents which have brought them
about, our “causes of variation ” (provided the effects
can be shown) may be in reality almost demonstrated.

Amongst the numerous influences and conditions, in
obedience to which the members of a large proportion
of the animate world would appear, at times, in their
outward aspect to be modified or fashioned, the following
may be selected as perhaps of primary importance :—

1. Climatal causes generally (whether dependent on
latitude or upon altitude).

2. Temporary heat or cold, of an unusual degree,

3. Nature of the country and of the soil.

4. Isolation, and exposure to a stormy atmosphere.

§ I. Climatal causes generally, whether dependent on
latitude or altitude.

Perhaps, judging superficially, climatal causes gene-
rally would appear to have more effect on insect deve-
lopment than any with which we are acquainted; yet,
powerful as they unquestionably are, experience teaches
us that such is not the case. In combination with other
modifying principles, hereafter to be noticed, they may
be (and probably are) exceedingly important; yet, when
taken singly and alone, we have no evidence to show
that their consequences are of such primary significance
as might be anticipated. Mr. Darwin, in describing the
fauna (which includes many mundane forms) of the
Galapagos Archipelago, situated immediately under the
equator, remarks: “ The birds, plants, and insects have
a desert character, and are not more brilliantly coloured
than those from Patagonia; we may therefore conclude,
that the usual gaudy colouring of the intertropical pro-
ductions is not related either to the heat or light of
those zones, but to some other cause,—perhaps to the
conditions of existence being generally favourable to
life*??

Although it is true, in a broad sense, that the nearer
we approach the Line the grander and more gorgeous
are the animate beings which tenant the surface of our
earth, there are at the same time so many exceptions to

this law, that it cannot be regarded as by any means
* Journal of Researches (London, 1852), p. 381.

24:

universal; and whatever, therefore, be our ideas on a
subject which might perchance seem to be self-evident,

we are compelled to infer that climatal causes, of them-
selves, will not suffice to account for the numerous cases
of aberration which we so constantly meet with in re-
presentatives of the same species exposed, through a
long series of centuries, to opposite conditions of atmo-
sphere. We need not, however, go so far as the Gala-
pagos to convince ourselves of this. The Madeiran
Group is placed between the 32nd and 33rd parallels of
north latitude, off the coast of Africa, and contains a
Coleopterous fauna (as hitherto ascertained) of about
550 species. Now 240 of these, at least, occur also in
Europe (many of them even in our own country) ;
hence, if a more southern climate may be presumed,
of itself, to exercise any very decided modifying influ-
ence on insect development, we have an amount of ma-
terial for comparison which should surely afford us some
definite and tangible result. My own experience in
those islands would tend to prove, that, amongst the
many aberrations from their northern types which are
there everywhere displayed, comparatively few of them
can be referred for explanation to causes strictly climatal.
I do not say that none can be thus accounted for; yet
I trust to make it obvious in the followmg pages that
there are even greater agencies at work than climatal
ones in regulating (albeit within prescribed limits, and
by slow gradations) the outward contour of the insect
tribes.

When viewed geographically, there are two heads
under which the insects of every individual area may be
classed: namely, those which were created within its
bounds, and which constitute its true aborigines (in the
strictest sense) ; and, secondly, those which have reached
ùt, either by ordinary migration over an intervening
land, or by accidental introduction through human or
other agencies. Now it is to the members of the latter
of these ideal divisions that we principally look for any
positive evidence, whilst discussing the causes of varia-
tion: since, by the nature of the case, we must have
identical, or at any rate closely allied species to reason
upon before any sound conclusions can be drawn con-
cerning them from the circumstances and conditions
to which they are severally exposed; and it is clear,
that the fact of creatures being specifically coincident,
and yet under influences remote, does, for the most part,
actually imply a transportation of them (from their
primeval centres) beyond the limits of a naturally
acquired range. Moreover, the avroyOoves of the soil
(if we may be excused the idiom) are in all instances
adjusted to the peculiarities of the region in which they
were formed; and, consequently, where they have not
(as very frequently happens) diffused themselves to a
sufficient distance from the birthplace of their kind to
be acted upon in two opposite manners from without,

the date which they supply, during our inquiry into
specific modifications as dependent on external disturbing
elements, cannot be very considerable.

ees ——

In spite of this severe distinction, however, which I
would urge between the insect aborigines of a country
and those which (whether by compulsion or not) have
colonized it, and of the preference which (as just stated)
must be given to the latter whilst investigating the con-
trolling principles of aberration, I would not wish to
reject in toto the testimony which the former likewise
may indirectly furnish,—especially under the present

section, in which climatal causes on a large scale have
to be taken into account. ‘True it is that we cannot
hope to descry physical results amongst phenomena
which are due to the creative force alone; yet we may,
in the contemplation of them, recognize such an amount
of design, or a primary adaptation to conditions from
without, as shall afford, through its permanence and

method, fresh presumptive evidence that the “ conditions”
themselves may have some inherent modifying power of
their own on the aggressors from other districts, in which
a contrary influence may perchance prevail, and for the
overspreading of which they were, in the beginning,
more peculiarly constituted and ordained.

It has been already mentioned (and, despite the ex-
ceptional cases which are to be found, it is in a general
sense true), that the splendour and extravagance of the
insect world attain their maximum within the tropics;
and that the nearer we approach the central heat, the
more and more unmistakeable is the existence of this
law. It has been also hinted, that when viewed on a
very extensive scale, we shall not derive much direct

assistance (whilst examining insect-variation, with re-
ference to climate) from the consideration of a fact thus
seemingly important, —since there are but few species
whose range is so comprehensive as to embrace, at the
same time, the equatorial and temperate regions of the
earth; and since, as lately suggested, it is not from a
comparison of the aborigines of countries far removed
that we can hope to derive much positive information
during our present inquiry. It may be useful however
to speculate, why the creative energy should have been
thus lavished, as it were, in the torrid zone, whilst the
fauna of the cold north is so unpretending and sombre.
I believe that in the. actual number, both of individuals
and species, which they contain, the difference is not so
great, between the two latitudes, as might be imagined ;
and that, were the minims of Scandinavia to be suddenly
magnified into the giants of Brazil, the Laplanders and
Swedes might stand a fair chance of being temporarily
alarmed: nevertheless, as regards the multitude and
eccentricity of her forms, there can be no question in
which field it is that Nature has ever delighted more
particularly to sport.

Laying aside, therefore, the numerical statistics from
our account, is not the exuberance of the tropics at once
responsive to the conditions imposed upon them? Do |
we ask why it is that the insect population is there —
moulded upon a type comparatively so colossal ?—let the |
redundancy of the vegetation reply. Have not, also, |
more rapid laws of putrefaction and decay been pre-

= ane Tee =

scribed than in our cooler clime; and can we imagine
that it was not in obedience to this decree, that larger
and more active scavengers were framed? The gaudy
wings that float idly on the breeze, and the coats of mail
which glitter m the light, have they nothing to tell of
the local circumstances around them; or, is it too much
to infer, that a more glorious and stimulating sun re-
quired creatures of superior brilliancy to bask in its
rays? A moderate degree of heat, and that only during
a certain portion of the year, may suffice in quiescent
regions to keep up the equilibrium of the organic world,
the various members of which, whether animals or
plants, are ensured, in such countries, their alternate
seasons of activity and rest ; but within the tropics, life,
in all its aspects, is ever vigorous; and, though the
several species may have their appointed times of partial
repose, there is no such thing as tranquillity for the
mass. Hence it is, that to meet the requirements of a
Flora * such as there obtains, a less magnificent Fauna
would have been inadequate; and we cannot but recog-
nize, that, in the wonderful and almost endless modifica-
tions of the insect tribes which people those zones, a

special provision has been made to check the overgrowth

of other created things.

* The great preponderance of the phytophagous over the pre-
dacious tribes, in the hotter regions of the earth, is a remarkable
fact, and strongly suggestive of the relation which the insect and
vegetable worlds (both of which attain their maximum in those
zones) bear to each other. “ The carnivorous beetles, or Carabide,”
says Mr. Darwin, “appear in extremely few numbers within the

But how, it may be asked, does this primary adapt-
ation to external conditions affect the question of spe-
cific development? Perhaps not much: nevertheless, as
lately urged, it is well that such adaptations should be
borne in mind, not merely that due importance may be
given to influences in conformity with which the creative
act was at the first expressly regulated ; but also that we
may be prepared, if any qualifying power be admitted to
reside in those influences themselves, for the kind of
aberration which reason and experience would seem
alike to imply that we should, in the various instances,
anticipate.

We have already stated, that climate, when taken

alone, does not appear to produce any very decided
modifying effect on insect form, seeing that there are!

vast numbers of species of a wide geographical range
which do not display, on their northern and southern
limits, differences sufficiently constant to be regarded as
purely climatal ones; and it is clear that, if climatal
causes of themselves were of real primary significance,
we should probably seldom fail to trace out, from their
long-continued operation, some steady and positive
result. Yet when combined with other principles, there

tropics. The carrion-feeders and Brachelytra are very uncommon ;
on the other hand, the Rhynchophora and Chrysomelide, all of
which depend on the vegetable world for subsistence, are present in
astonishing numbers. The orders Orthoptera and Hemiptera are
peculiarly numerous; as is, likewise, the stinging division of the
Hymenoptera, the bees, perhaps, being excepted.”—Journal of
Researches, p. 34.

is evidence that a considerable amount of influence must
be conceded to the action of mere heat and cold, work-
ing permanently and according to fixed laws, on the
members of the insect world. Such being the case, it is
perhaps not surprising that a slight difficulty should
arise, through our employment of separate sections under
which to examine the causes of variation; for, since it is
ordinarily by the union of several disturbing influences
that aberrations are brought about, it is for the most
part impossible to refer the results, however con-
spicuous they may be, to a solitary controlling element.
And hence, though we may be able at times to point
out perchance the single reason for certain phenomena,
with comparative precision, it will generally happen that
two or three agents must be appealed to before we can
arrive at a conclusion by any means satisfactory. I
would. desire, therefore, that the examples hereafter to
be noticed may be judged of in the mass; and may not
be considered. as severally assigned, of necessity, to an
isolated deranging cause, through the fact of their being
placed, for the sake of convenience, and because of the
predominance which special controlling principles have
had in maturing them, under sections, both, as it were,
exclusive and particular.

That climate of itself possesses but a limited modify-
ing power on insect development, is evident from the
consideration (just alluded to), that numerous species of
comparatively wide distribution are totally unaffected by
it. Thus, for instance, the Pissodes notatus, Fab., a weevil

əl

which occurs in pine forests from Lapland to Barbary,
and which has been naturalized even in the Madeira
Islands, passes through the alternations to which it is
specifically subject, irrespective of country. In like
manner, the Lixus angustatus, Fab., so abundant in Cen-
tral and Southern Europe, the north of Africa, Malta,
Madeira, and the Canaries, and which has been detected
in Persia, would seem to be perfectly free from atmo-
spheric control. The Coccinella 7 -punctata, Linn., which
exists in nearly every portion of the Old World, is
apparently unacted upon geographically. Numberless
beetles which follow in the track of man, or at any rate
are liable to do so, almost everywhere (such as Carpophilus
hemipterus, Linn., Trogosita mauritanica, Linn., Lemo-
phlæus pusillus, Schönh., Dermestes vulpinus, Fab., Ano-
bium striatum, Oliv., Rhizopertha pusilla, Fab., Sitophilus
granarius and Oryze, Linn., and Tribolium ferrugineum,
Fab.), show little or no tendency to variation. Noris this
independence of climate to be observed less frequently m
the aquatic forms, than in the terrestrial ones: the Aga-»,
bus bipustulatus, Linn., common in the streams and pools
of the whole of Europe, the north of Africa, and in Ma- |

deira, although naturally somewhat inconstant, offers no

aberration, the result of latitude; as is equally the case |
with the Hydroporus confluens, Fab., which is found from
Sweden to the Canaries, and the Eunectes sticticus,
Linn.,—an insect literally cosmopolitan. The Swallow-
Tail Butterfly (Papilio Machaon, Linn.), the Clouded
Yellow (Colias Edusa, Fab.) and the Painted Lady (Cyn-

thia Cardui, Linn.) ,—the first and second of which occur
throughout Europe, in Siberia, Syria, Egypt, Barbary,
Nepaul, and Cashmere ; whilst the third (so general in
our own country) has been recorded from India, North
America, the Brazils, Africa, Java, and New South Wales,
—however irregular they may be, afford no indications*
of undoubted geographical instability.

We need not however multiply examples, since our
space will scarcely admit of it, and numbers of them will
be at once suggested to the entomologist : what it mainly

concerns us here to corroborate, is the thesis, that cli-
matal operation, although by no means invested with a
universal qualifying power, kas an amount of influence on
certain species, even whilst unconnected with other ele-
ments,—and therefore, à fortiori, when in combination
with them.

The two principal conditions on which climatal causes
generally may be said to rest, are latitude and altitude.
As regards the former of these, however, whilst the
equatorial and arctic regions of the earth will of course
give us the extremes of heat and cold, we shall often
perceive differences of temperature (the result perhaps of
local circumstances) in areas but slightly removed from
each other, sufficient to affect very materially, though
by what means it is difficult to understand, the outward

* Mr. Westwood states that he possesses an individual of the
Papilio Machaon from the Himalayan Mountains, captured by Pro-
fessor Royle, “which scarcely exhibits the slightest differences

when compared with English specimens.” — The Butterflies of Great
Britain, p. 4.

contour of the insect tribes. Thus, to go no further
than Ireland, we find that the specimens of Silpha
atrata, Linn., so abundant throughout England and the
whole of Europe, have put on (it may be from the moist-
ure of the atmosphere, or from some other obscure \
influence) the appearance of a distinct race,—so distinct |
indeed as to have long received another name, S. subro- .
tundata, from British naturalists. I think it far from
improbable that the Tachyporus nitidicollis, Steph., an’
insect eminently characteristic of that country (and one
on which I have lately offered some remarks*), is but a
darker climatal modification of the common T. obtusus :

and it is well known that the examples of Pelophila
borealis, Payk., from Killarney and Loch Neagh are per-
manently larger, and much more metallic, than those |

from the Orkneys. The Nebria complanata, Linn.,
assumes a more pallid hue in the neighbourhood of
Bordeaux than it does on the sandy coasts of Devonshire
and Wales: and I have but little doubt that the Oma-
seus nigerrimus, Dej., of Spain, the north of Africa, and
Madeira, is a geographical state of the O. aterrimus of
Central Europe. The Sitona gressoria, Tilig., so univer-
sal throughout the Mediterranean districts, Madeira and
the Canaries, may be but the subaustral form of S. grisea.
The Bembidium obtusum, Sturm, is shorter and less
parallel in our own latitude than it is in the Madeiran
group and along the Mediterranean shores : whilst the
Holoparamecus niger, Aubé, of Madeira and Sardinia is
* Zoologist, xiii. p. 4655.
c5

very much paler than the same beetle when taken in
Sicily. Specimens of Pieris Brassice, Linn. (the White
Cabbage-Butterfly,—an insect of widely acquired range),
from Nepaul and Japan, are recorded* to have differed
so strongly from the ordinary European type as to have
been referred, by Boisduval, in doubt to that species.
Mr. Westwood has received the Vanessa Atalanta, Linn.,
from North America, receding slightly from its British

analogue ; but which he, nevertheless, does not regard
as specifically distinct : and such also (he adds) was the
opinion of Mr. Kirby, who has described his American
examples under that name. The common Hipparchia
of Madeira I believe to be a fixed geographical modifica-
tion of the H. Semele, Linn., of our own country,—in
which the paler bars of the upper surface are evanes-

cent ;—there are, however, I imagine, but few entomo-
logists who would concur with me in this hypothesis.
The Madeiran specimens of Lycena Phiwas, Linn. (the
Small Copper Butterfly), are invariably darker, and more
suffused, than the English ones: and Mr. Westwood re-
marks that he possesses examples from North America
which “ differ in the decided black spotting of the under
side of the hind wings, in the bright red streak near
their hind margin, and in wanting the minute spot on
the costa of the fore wings ; but that these characters can
scarcely be held to constitute a distinct species.”

Few observers can have failed to remark, that increased

* The Butterflies of Great Britain (London, 1855), p. 17.
F Id. p. 94.

altitude frequently corresponds, both in its fauna and
flora, to a higher latitude; and that, consequently, if we
ascend the mountains of a southern land, we shall be
struck, at times, by the presence of a host of species
which obtain at a lower level in more temperate zones.
This is peculiarly traceable in the Madeira Islands,—
which, from their subaustral position, and height (the
loftiest peak of the central mass exceeding 6000 feet
above the sea), afford a rich field to the student of zoo-
logical geography. Yet, though the degrees of mere
heat and cold are such as to allow, in the two cases,
species positively identical to flourish ; we should surely
anticipate some slight change from the different atmo-
spheric conditions (especially when in union with other
circumstances) to which they have been, through a lapse
of ages, respectively exposed: it may be well there-
fore to inquire, whether experience does at all tend to
strengthen what our reason has an à priori inclination
to endorse. It must be recollected however that, in the
instances to which we would draw attention, small aber-
rations are all that can be usually looked for, since climate
of itself does not appear to be very potent in its action.
We should remember, also, that the boundaries of insect
instability are restricted; and, although we would advo-
cate freedom of development within limits which are
more or less comprehensive according to the species, to
pass beyond them would be confusion, and such as could
result from a lapsus Nature only, rather than from a

power of legitimate variation.

Tn exact conformity with what the above remarks will
| have prepared us for, we find that the Dromius obscuro-
guttatus, Dufts., of Central Europe, has undergone on
| the mountain summits of Madeira changes precisely to
that extent which we should have calculated upon; and
although they would seem in reality to be referable to
climate and isolation combined, yet, since it is not
always possible (as lately stated) to treat the elements
of disturbance separately, and it is my object in this
short treatise to bring forward a few prominent examples
in support of the considerations proposed, rather than to
accumulate a mass of material for the registry of which
my space would be inadequate, I will quote in extenso
the reflections which, during the compilation of the
< Insecta Maderensia,’ suggested themselves tome. “The
Dromius obscuroguttatus is a common European insect,
and the Madeiran specimens recede from the ordinary
ones in being slightly larger, and in having their elytra
more obscurely striated, with the humeral patch less
distinct: their entire surface, moreover, is of a deeper
black, a difference which is especially perceptible on the
legs. It occurs in the greatest profusion in Madeira
proper, though only from about 5000 to 6000 feet above
the sea. Although so common throughout Europe, it

is perhaps, when geographically considered, one of the

most interesting of the Madeiran Coleoptera, as affording
a striking example, not only of the modification of form
in a normally northern insect when on its southern
limit, but as showing likewise how a species, abundant

on the low sandy shores and sheltered sea-cliffs of more
temperate regions, finds its position here only on the
summits of the loftiest mountains. It is true that the
aberration from the typical state is not in the present
instance very considerable ; yet when the circumstances
producing it are taken into account, I am persuaded
that the difference is exactly of that nature on which too
great stress cannot possibly be placed, when discussing
the general question of geographical distribution as

having a tendency, more or less directly, to affect both

colour and form. It is well known to naturalists that a
multitude of insects from the New World, receding from
their European analogues merely in certain excessively
minute characters, have usually been pronounced at once
as new to science, first because those differences are con-
stant, and secondly because the specimens have been
received from the other side of the Atlantic. And yet
in instances like the present one,—in an island which,
while it belongs artificially to Europe, is yet naturally
sufficiently distinct from it as to form at any rate a
stepping-stone to the coast of Africa and the mountains
of Barbary,—species similarly circumstanced are not
necessarily received as new (and rightly so, I apprehend),
though in every respect affording differences not only
analogous to those already mentioned, but in many in-
stances positively identical with them. Tf, however, a
specific line of demarcation does of necessity exist be-
tween the creatures of the Old and New Worlds, the
problem yet remains unsolved, so long as intermediate

a
Taree ANA rreme oeae

Caan

ES ————

islands present parallel modifications, where that line
is to be drawn. Meanwhile, how far geographical va-
rieties of this kind, concerning the non-specific claims
of which confessedly but little doubt can exist, may lead
to the explanation of the Transatlantic ones just referred
to, I will not venture to suggest. Yet certain it is, that
the one case bears directly on the other; and that, if
we can prove that common European insects, when iso-
lated in the ocean, become in nearly all cases more or
less modified externally in form, there is at least pre-
sumptive evidence that the law will hold good on a
wider scale, and may be extended, not only to the
Atlantic itself, but even to countries beyond. The dif-
ferences of the present Dromius from its more northern
representatives are, as just stated, small; nevertheless,
since they are fixed, those naturalists who do not believe
in geographical influence might choose to consider them
of sufficient importance to erect a new species upon.
But after a careful comparison of this with other insects
similarly circumstanced, I am convinced that the modi-
fications in question are merely local ones, and such
as may be reasonably accounted for by the combined
agencies of latitude and isolation, and the consequently
altered habits of the creature, which is thus compelled
to seek alpine localities in lieu of its natural ones*.”

In like manner the Calathus fuscus, Fab., the Ancho-
menus marginatus, Linn., and the Anthicus fenestratus,
Schmidt, which occur almost exclusively in the lower

* Insecta Maderensia (London, 1854), pp. 7, 8, 9.

regions of northern latitudes, are found in Madeira on
the mountain tops ; each, moreover, possessing characters
which are just sufficient (although slight) to distinguish
them from their European representatives.

And if we inquire, on the other hand, into the abo-
riginal species of those islands,—or, at any rate, into
such of them whose naturally acquired range embraces
the opposite extremes of atmosphere,—we shall detect no
less surely (albeit within a narrower space) the result of
climatal action on insect form. The Helops confertus,
Woll., “varies according to the altitude at which it is
found; being usually deeply striated and rugose on its
lower, but subpicescent and much more lightly sculptured

on its upper limits. I have taken specimens indeed on
Pico Ruivo, and on the mountain-plain of the Fateiras,

which are so far diminished in roughness as almost to
resemble, at first sight, the H. Pluto*.” The Pecte-
ropus Maderensis, Woll., which ranges from about 2500
feet above the sea to the summits of the loftiest hills,
although usually with pale legs, is distinguished by
having its femora almost invariably dusky when on
its highest elevation ; and, following out the analogy
with that beetle, the Trechus alticola, Wol., should
perhaps be regarded as an alpine state of the T. custos.
The Calathus complanatus, Koll., assumes along the up-
land heights a very different aspect to what it does in the
regions below, being generally more piceous and convex,
altogether broader (in proportion) and shorter, and

* Insecta Maderensia, p. 516.

with doth sexes (though, of course, especially the male)
shining.

Nor is this principle of topographical variability (the
result of climate) less apparent in other countries also.
The Notiophili, for instance, “are extremely unstable,
both im their sculpture and hue, being subject to con-
siderable local modifications, though more particularly
affected, it would appear, by altitude. Thus, in our own
country, the N. semipunctatus, Fab., one of the common
representatives of the plains, is found likewise on the
summits of the mountains; but at that elevation it be-

comes liable to great alternations of colour, ranging

from pale brassy-brown, with the apex testaceous, into
deep black. The sculpture, however, perhaps is nearly
as much dependent on other circumstances for its mo-
dification as upon altitude, since it seems tolerably clear
that proximity to the sea-shore, especially where the
localities are saline, will frequently produce a more
faintly impressed surface*.”’ It has indeed been lately
suggested, that the Helobia nivalis, Payk., may be per-
haps, after all, but a mountain variety of the H. brevi-
collis ; the Leistus montanus, Steph., of the L. fulvibarbis,
and the Patrobus septentrionis, Dej., of the P. excavatus ;
but of this I think further proof is needed, seeing that
certain species do appear to exist which are strictly
alpine (that is to say, which have not been, severally,
detected in the lower regions, of more northern zones) ;
and, in most instances, where aberrations are to be met

* Tnsecta Maderensia, p. 17.

with from the effect of altitude, we have a right to
inquire (provided the types from which they are sup-
posed to have originally sprung obtain in the less-
elevated portions of the same country), where are the
intermediate links? Now I am not aware that any such
links have, in the examples above cited, ever been ob-
served; whilst I can vouch that in at any rate many
districts where the quasi variety is found, the descend-
ants of its assumed progenitor do occur in the plains
beneath. I have remarked that the Cicindelide often
become inconstant in colouring as they approach their
maximum of height above the sea; and I have but
little doubt that the C. fasciatopunctata*, Germ., from
Asia Minor and Turkey, is the C. sylvatica modified by
a long residence in elevated regions. And so it is with
the Chrysomele, many of which become, in the loftiest
altitudes to which they ascend (as I have noticed at the
head of the St. Gothard Pass of the Swiss Alps), subject

to unusual changes, both in lustre and hue.

The above examples, although few and indiscriminately
selected, will serve to illustrate the principle which we
have been contending for,—that climatal influences
generally, may (and in most instances do) tend to affect,
more or less directly, the outward contour of the insect
tribes. It will be remarked that, in the cases hitherto

= * T possess specimens of this insect captured on the summit of
Mount Olympus by my friend E. Armitage, Esq., who is also of
opinion that it may be but a mountain state of the C. sylwatica,
Linn.

cited no great disturbing power has been made evident,
—the aberrations to which we have appealed being,
most of them, comparatively minute. This, however, is
simply in harmony with the belief which we have already
expressed, that climatal causes, when taken singly and
alone, are not of primary importance whilst discussing
the question of specific modification. It remains for us,
in the following sections, to inquire, whether there are
any other elements at work from which greater results
are to be expected. Meanwhile, let us not forget that
differences may be, in the strictest sense, significant,
even whilst small; and that it is their constancy, rather
than their magnitude, which more particularly concerns
us in the present treatise, seeing that it is with reference
to those distinctions which are less conspicuous that the
greatest amount of misunderstanding (through the fact
of their being fixed) usually prevails; whilst it is our
main object to show that dissimilarities do not neces-
sarily imply the specific isolation of the creatures which
display them, merely because they are, in their several
localities, permanent.

pus Temporary heat or cold, of an unusual degree.

It is perhaps unnecessary that the action of temporary
heat and cold, of an unusual degree, should be considered
under a separate head from that of climatal causes gene-
rally; nevertheless, since the latter are, in a certain
sense, permanent in their operation, it may be thought

desirable that I should offer a few words on the effect of
sudden exceptions to the ordinary routine of things,
such as, for instance, seasons of peculiar intensity. It
does not however appear that any very important modi-
fications do often occur from conditions thus abnormal,
and as it were accidentally brought about: on the con-
trary, indeed, it is a well-known fact, that the members
of the insect world are singularly independent of such
contingencies; and that, in the same manner as their
times of maturation are neither hastened nor retarded
by them, their external development is for the most
part free from their control. Yet, in spite of this,
specific results are wont to happen, ever and anon, from
such circumstances, as though it were a fundamental
- axiom, that every agent which Nature can press (regu-

larly or irregularly) into her service should have, though
it may not always exercise its privilege, some qualifying

voice.

I believe that almost the only deviation from the
_ typical state, in insect form, which has been observed to
originate, par excellence, from the occasional continu-
ance of undue heat or cold, is curiously enough an or-
ganic one,—having reference to the enlargement of the
wings. Every entomologist must be aware that a vast
proportion of the Coleoptera (especially the Carabide)

are subject to great inconstancy in their metathoracic , |

organs of flight. Many species, as the common Calathus \
mollis of our own country (to which my attention has
been more particularly drawn by the Rev. J. F. Dawson),

have the hind wings at one time ample, at another rudi-
mentary, and at a third nearly obsolete. Now, although
other causes, hereafter to be noticed, would seem to have
far greater power than climatal ones in permanently
regulating the size and capacity of these appendages; I
think it will be found on examination (and I may add
that Mr. Westwood is of the same opinion *), that the
greater or less development of them may be frequently
explained by the unusual severity of the seasons. My
own researches would certainly tend to prove, that heat
does (in the main) favour, and cold retard, their pre-
sence. Exceptions (often rendered intelligible from
the evident working of counter influences) will of course
arise in abundance to this hypothesis ; yet my impression
is that, upon a broad scale, it will stand the ordeal of a
rigid inquiry.

Speaking of certain representatives of the Hymen-
optera (Chalcidide), Mr. Westwood observes: “A
curious peculiarity exists in one at least of these
apterous species, which has been noticed by no previous
author, namely, Choreius ineptus, Westw., which,
although ordinarily found in an apterous state, was
discovered by me in considerable numbers during the
hot summer of 1835, with wings+”. And, touching
the irregularity of the alary organs in the Homopterous
Fulgoride, he remarks: “ Other instances, in which the

wings undergo a deficiency of development, occur in the

* Tntroduction to the Modern Classification of Insects (London,
1840), i. p. 473. + Id. ii. p. 158.

genus Delphax, the majority of which, in our English
species, have the upper wings not covering more than
one half of the abdomen,—the terminal membrane
being deficient, as well as the hind wings. In certain
seasons, however, especially hot ones, the wings are
fully developed*”. Mr. Curtis has indeed formed the
undeveloped specimens into a different genus, Crio-
morphus.

Although the result of a more stimulating sun may
be often neutralized by that of isolation (which, as we
shall hereafter see, is a resistless agent, amongst a host
of species, in weakening, and frequently rendering abor-
tive, the powers of flight) ; yet heat, when freed from
counter influences, may be traced in its permanent effect
on the alary system of insects, no less than when tem-
porarily applied. The consideration of this, however,
belongs strictly to the preceding pages, and we will not
therefore discuss it here. The common Bed-bug (Cimes
lectularius, Linn.) is almost invariably apterous, or with
very short rudimental hemelytra; yet Scopoli (Ent.
Carn. p. 354) mentions its occurrence with perfect
wings. Fallen, also, and Latreille, state that it has

been found winged; whilst Westwood remarks that it |
has been reported as occasionally winged in the East/

Indies ; and it would seem extremely probable that, in/

these examples, as in numerous others which are on
record, we may detect the consequences of heat ; either

* Introduction to the Modern Classification of Insects, i.
p. 431.

as temporarily applied (in an unusual degree), or
through the accidental transportation of the insect into
a naturally warmer atmosphere.

§ III. Nature of the country and of the soil.

Before we proceed to inquire to what extent the out-
ward aspect of insects is liable to be controlled by the
physical state of the areas in which they severally
obtain, it may not be altogether out of place to offer a
few reflections on the superiority which some regions
possess intrinsically over others, both for the increase
and diffusion of the animal tribes. To suppose that all
countries within the same parallels of latitude are
equally favourable for the development of life (not to
mention the after-dispersion of it), is contrary to experi-
ence; for although (as we have already pointed out) the
organic world does certainly, when viewed in the mass,
approach its maximum as we near the tropics, there are
at the same time so many violations of this law, that we
cannot admit its operation except in a broad and general
sense.

In a former section of this chapter, I drew attention
to the fact, that certain islands, equatorial and subaustral,
are anything but suggestive of their actual positions
with respect to the line of central heat on the surface of
the earth. It was with regard to climate alone, however,
that I wished them to be understood: and it is not

until now that I have ventured to urge the necessity of

taking other influences into account also, if we would
desire to recognize anything like design and adaptation
(I will hardly call it cause and effect) between the con-
tinent and the thing contained. It is almost needless to
add, that there are many elements to be considered,
such as local atmospheric conditions, excess or deficiency
of electricity, superabundant moisture, diminished light,
and the geological composition of the soil, before we
can hope either to appreciate zoological phenomena as a
whole, or to reconcile the apparent inconsistencies which

they are accustomed to display.

Mr. Darwin, to whom we are indebted for so much
valuable information concerning the natural history of
various portions of the world, in his notes on Tierra del
Fuego, observes: “ Beetles occur in very small num-

bers ; it was long before I could believe that a country
as large as Scotland, covered with vegetable productions
and with a variety of stations, could be so unproductive.
The few which I found were alpine species of Harpalide
and Heteromera, living beneath stones. The vegetable-
feeding Chrysomelide, so eminently characteristic of the
tropics, are here almost entirely absent. I saw very few
flies, butterflies, or bees, and no crickets or Orthoptera.
In the pools of water I found but few aquatic beetles.
I have already contrasted the climate as well as the
general appearance of Tierra del Fuego with that of
Patagonia; and the difference is strongly exemplified in
the entomology. I do not believe they have one species
in common; certainly the general character of the

insects is widely dissimilar *.” Now, it is impossible to
read this account without being at once struck with two

primary considerations : first, that there must exist some

great peculiarity (apart from climate) in a region the
fauna of which is thus singularly constituted; and,
secondly, that latitude (however important it may be in
a comprehensive point of view) must exercise in this
case a very secondary influence, to allow of localities
separated only by the Straits of Magellan to present
differences thus extraordinary.

Although so dissimilar in many respects, Madeira
and Tierra del Fuego have evidently much in common
as regards the conditions which they afford for the
increase of organic life. Mr. Darwin describes the latter
as “a mountainous region, partly submerged in the
sea.” So is Madeira. He also adds, that it is “ covered
to the water’s edge with one dense, gloomy forest ;”
that “to find an acre of level land in any part of the
country is most rare ;” and that “ within the forest, the
ground is concealed by a mass of slowly putrefying
vegetable matter, which, from being soaked with water,
yields to the foot.” Such was Madeira, in its normal
state}; and such it still is throughout a large district

* Journal of Researches, p. 238.

+ That I may not be misunderstood by those of my readers who
conceive Madeira to be a kind of “ arva beata,” with the sky for
ever blue, and (as a consequence) an unclouded sun; I would re-
peat, that I am not speaking of the vicinity of Funchal only (from
which the invalids, who resort thither for their health, almost
exclusively draw their deductions), but of Madetra,—and, more-

towards the northern coast. I cannot indeed refram
from quoting the following, since it portrays the cha-

over, of Madeira as it was, and not of Madeira as it is. More or
less of cultivation during a period exceeding four centuries, in con-
junction with the overwhelming fire which completely devastated
the entire south of the island, immediately after its first settlers had
taken possession of it, and which is stated (in the accounts which
are transmitted to us) to have smouldered on for nearly seven
years, have so altered the features of the country, that it is only m
the untouched regions of the north (on which the woodman’s axe is
nevertheless encroaching, season after season, with lamentable
rapidity) that we can catch even a glimpse of its pristine condition.
The dense forests which then everywhere abounded must have
caused an amount of moisture and exhalation of which even the
northern districts as they now are (though saturated, even yet, with
dampness; and at a certain elevation almost constantly enveloped
with clouds) can give us but a faint idea. So tremendous indeed
must have been the aqueous accumulations which then hung
around the island, that even the splendour of a southern sun cannot
have penetrated the atmosphere as it does at present; and, hence,
the historical fact that Madeira proper (although separated by a
channel of only thirty miles in breadth, and now usually visible in
bold relief against the sky, during a portion, at least, of every day,
from a far greater distance) was not discovered for an entire year
after the colonization of Porto Santo, on account of the thickness of
the canopy which shrouded it from view, is at once rendered in-
telligible. It is narrated, that, in the year 1419, Prince Henry of
Portugal organized an expedition to attempt the doubling of Cape
Bojador ; but the commanders, having lost their reckoning, were
driven ashore on an island,—which they named Porto Santo. in
commemoration of their escape from the perils of the sea. “On
their return,” says Mr. Harcourt, “ Prince Henry sent out Zargo,
Vaz, and Pestrello, to plant a new colony in the island. It was not
long before a dark spot was observed on the western horizon of
Porto Santo. This was regarded by some with superstitious awe ;
but Zargo concluded it to be clouds attracted by high land; and

racteristic features of Madeira so vividly, as to be, lite-
rally, as suggestive of that island as it doubtless is of
Tierra del Fuego. “Finding it nearly hopeless,” says
Darwin, “to push my way through the wood, I followed
the course of a mountain-torrent. At first, from the
waterfalls and number of dead trees, I could hardly
crawl along; but the bed of the stream soon became a
little more open, from the floods having swept the sides.
I continued slowly to advance for an hour along the
broken and rocky banks, and was amply repaid by the
grandeur of the scene. The gloomy depth of the ravine
well accorded with the universal signs of violence. On
every side were lying irregular masses of rock and torn-
up trees; other trees, though still erect, were decayed
to the heart and ready to fall. The entangled mass of
the thriving and the fallen reminded me of the forests
within the tropics; yet there was a difference,—for in
these still solitudes, Death, instead of Life, seemed the
predominant spirit *.”

As regards the paucity of species in Tierra del Fuego,

there are many instances on record of other countries,
and in various latitudes, in which the same anomaly
(though perhaps in a less degree) prevails. I have my-
self observed, in Madeira, large forest tracts, at a con-

shaping his course in that direction, in spite of the endeavours of his
crew (by menaces and supplications) to prevent him, he discovered,
in the year 1420, the island to which, from the trees that covered it,
he gave the name of Madeira.”—A Sketch of Madeira, London,
1851, p. 16.

* Journal of Researches, pp. 209, 210.

siderable elevation above the sea, and which are so
densely clothed with wood as to be scarcely penetrable,
almost destitute of insect life. Around such altitudes
however the clouds perpetually cling, and the rain is
well nigh incessant; and it would seem as if the very
dampness which causes the vegetation (especially the
ferns) to flourish in such rank luxuriance, and the timber
to rot with such rapidity that the gigantic trunks are
washed, reeking with moisture, down the mountain-
slopes, was too extreme for animal existence.

Now, it will be remembered that the Madeiran group
is situated at a corresponding distance from the Equator
as Morocco, Algeria, the lower limits of Syria, Texas,
and Upper Florida are,—all of which literally teem with
life; and that Tierra del Fuego lies between the same
parallels of south latitude as Durham and Central Russia
do in the northern hemisphere. From which it is
evident, that the equal removal of countries from the
earth’s greatest heat does not necessarily imply an
equal exuberance in their Faunas,—seeing that in both
the regions just appealed to, we not only perceive a vast
difference in the. numbers of the insects which they re-
spectively contain, from those in other districts which
have a similar divergence from the tropics; but we are
even able to recognize a certain resemblance of physical
conditions (and, therefore, of the creatures which have
been either adapted to, or modified by, them) in lands
so far asunder, not merely with respect to latitude, but

longitude also, as Madeira and Tierra del Fuego.
D2

Other instances might be cited, in support of the im-
mediate principle for which we are now contending,—
namely, that many areas have (from local circumstances)
a natural superiority over others for the increase of the
animal tribes, even apart from the direct action of heat
and cold :—but space will only permit me to glance at a
very few of them. We may detect evidences of this fact,
in Ireland; which, in spite of the narrowness of the
straits which separate it from our own country, and of
its independent commerce with all parts of the civilized
world, has an insect fauna curiously limited. From
what cause this may arise,—whether from some obscure
physical influences peculiar to the soil, or (as Professor
E. Forbes has suggested) from the sudden impediment
which the establishment of St. George’s Channel pre-
sented to the westward progress of the various species
from the Germanic plains,—it is difficult to speculate :
yet the fact of its poverty remains, and we must explain
it as best we are able. There can be no question, that,
from more frequent communication with England, its
entomological fauna has of late years been considerably
increased; and it is equally easy to detect, through an
examination of its less inhabited provinces, that at a
period geologically recent its insect population must
have been singularly scanty. I know of few regions
(not even excepting the uplands of Madeira) which are
more deficient in insect life than the mountains of
Kerry. Although abounding, throughout extensive di-

stricts, with wood and water, and presenting every appa-

rent requisite for its full development; the naturalist
will often be disappointed by finding that a hard day’s
work has not ensured him the same amount of success
as he would have reaped in less than half an hour in
many an English meadow. Do we ask, why this is so?
—it is impossible to reply, except on the supposition
that there are real physical agents, independently of
heat and cold, which are unfavourable in Ireland to the
existence of these lower creatures. We may perhaps be
told, by the advocates of Professor Forbes’s theory, that
it is the result of isolation,—the quondam land of pas-
sage having been broken up before the proper comple-
ment of species had reached this large portion of their
western destination. But even this, although I believe
it to contain much presumptive truth, will not alto-
gether suffice to account for the phenomena which we
see; for Ireland is not only remarkable for the paucity
of its species, but also for the paucity of its individuals,—
and the latter fact cannot be explained by any stretch of
the migration-hypothesis. We are compelled therefore
to conclude, that Ireland, like the other countries to
which we have already alluded, presents conditions
(altogether irrespective of latitude) which must be re-
garded as adverse to the general prosperity of the insect
races.

And so it is with localities (no less than with larger
countries),—many of which are eminently unproductive,
when compared with others situated at but a short
distance from them. Thus, the south-western corner of

England is by far the most unprofitable portion of our
island, unless indeed I am much mistaken, for insect
ascendency. I have made some remarks on this subject
in the ‘Zoologist, —from which I extract the following :
“ Unlike the easy collecting to which we are accustomed
in the more favoured East, miles of unprofitable country
have often to be gone over, be it swampy moorland or
iron-bound coast, where scarcely an insect is to be seen ;
or, at any rate, where the few which exist are so ordi-

nary, and so sparingly dispersed, as to be scarcely worth
the labour of obtaining them,—more especially since the
identical species are many of them to be met with in
the utmost profusion in more central, or eastern districts.
Whether it be the moisture of the climate, or the vio-
lence of the south-west winds, which (continually sweep-
ing, as they do, over the high central mass of Devon-
shire and the bleak, barren downs of Cornwall) present
as great an obstacle to the development of animal, as
they clearly do of vegetable life, I will not venture to
suggest ; yet certain it is, from observation, that insects

not only become fewer in number in proportion as they
are exposed to these external agencies of wind and water ;
but likewise, in many instances, diminish so consider-
ably in stature as to be scarcely reconcileable with their
normal types*.”

TA There can be no doubt that islands are, for the most

‘a - : i
| | part, more unproductive (even in proportion) than con-

1 |

| | tinents; and that, the smaller the area, the less favour-

|
Í

a * Zoologist, x. 3616.

able will it be for the development of insect life. Mr.
Darwin has noticed this fact in the Galapagos (which he
remarks are only equalled by Tierra del Fuego, in bar-
renness), on Keeling Island (in the Indian Ocean), where
he succeeded in detecting but thirteen species, in St.
Helena, and at Ascension; and I have added fresh
evidence to the same in the various portions of the Ma-
deiran Group*. It is however to geological causes that
we must mainly look for the explanation of this phæno-
menon; and, therefore, since I propose to examine that
branch of our subject in a future chapter of this treatise,
we will not discuss it now. It will also be better per-
haps to defer for the present the general question of
self-diffusion, which, at the opening of this section, we
proposed to consider, along with that of insect product-
iveness (as dependent on other local influences, besides
climatal ones), —it being scarcely possible to render the
problem of dispersion in any degree intelligible without
calling in geology to our aid.

* Considering that I have already detected more than one thou-
sand species in those islands, it may perhaps be questioned whether
the same truth is to be gathered from the result of my Madeiran
researches. I would wish it therefore to be understood, first, that
my statement refers to that group as contrasted with countries in a
similar latitude; and, secondly, that its real fauna is alone taken
into account,—the host of introductions from more northern regions,
a large proportion of which have probably taken place within a very
recent period (as may be fairly presumed from the knowledge that
fresh arrivals, an almost necessary consequence of the importation
of plants, are ovcurring nearly every season), having been dismissed
from our present inquiry.

Having then disposed of this preliminary appendage to
our inquiry, by expressing our belief (which I am satisfied
that observation will tend more and more to corroborate)
that certain countries and spots are by constitution more
favourable than others for the increase (apart from the after
dissemination) of the insect tribes,—and that too through
local influences amongst which mere heat and cold are
but secondary in importance ; let us proceed to consider,
how far the nature of the several districts may assist us
in accounting for some of those numerous aberrations
from the typical state which various insects are accus-
tomed to display, and on which it has too often hap-
pened that “species” (so called) have been attempted
to be established. I may premise however, that, whilst
(as already urged) I would regard climate per se as sub-
sidiary to many other agents, I would not wish ‘to
ignore its action altogether even under the present sec-
tion, since in combination with peculiar circumstances
and conditions it may have (and probably has) consider-
able controlling power: nevertheless I would desire it to
be looked upon here as, at any rate, an inferior element,
and as working in conjunction with physical influences
of greater significance than itself. If therefore under the
preceding heads it has been treated (so far at least as the
exceptions would permit) as a great geographical principle,

possessing a certain modifying quality on a large scale,
let us now merely recognize it to the extent in which we
are actually compelled to do, when dealing with areas of
smaller magnitude,—namely as a topographical one.

From amongst the many results which I have been
long accustomed to associate (whether rightly so, or not,
I leave it for others to decide) with certain special situa-
tions, I would draw attention to the singular incon-
stancy which numerous insects are liable to when ex-
isting on the coast,—and which frequently causes them
to assume an aspect so permanently different from their
inland types, that, without local knowledge to guide us,
they might be supposed at first sight to be specifically
distinct. Ten years ago I offered a few comments on
this fact in the pages of the ‘Zoologist’; which, as I
have seen no reason subsequently to modify them, I will
transcribe at length :— 7

“The extraordinary changes which many insects are
subject to when occurring near the sea, is a fact worthy |
of notice, and one which I do not remember to have
seen recorded. The strictly maritime species must be
left out of the question ; for although many of them are
exceedingly variable both in size and colour, still we
have no means of ascertaining whether that variation is
referable to the locality in which they are placed,—tor,
never being found inland, nobody can have an opportu-
nity of asserting that the same changes would not take
place, were they to occur in positions far removed from
the influence of the sea. When we find, however, the

same insects in profusion both inland and on the coast, )

and observe also numerous and marked deviations from |
the typical forms peculiar to the latter situation; then, |
à priori, we have strong presumptive evidence that the /

changes in question are the result of local circumstances,
and not referable to chance. ‘The alteration in size I
have almost always observed to be from large to small,
and scarcely ever the reverse; whereas in colour the
change takes place very nearly as much from light to
dark as it does from dark to light: nevertheless the
majority of instances I possess come under the latter
department. It has been remarked that all the speci-
mens of Mesites Tardii, which I captured in Devonshire,
were much smaller than the original series taken by
Mr. Tardy at Powerscourt Waterfall, in the county of
Wicklow ; and so decided was the difference, that many
of my friends, at first sight, concluded the two to be
distinct species. This, however, I consider entirely
owing to their locality, for my specimens were found
only on the coast, and Mr. Tardy’s at a considerable
distance inland. And, inasmuch as neither of these
instances rested on mere individual examples, but on
long and conspicuous series, the certainty of the change
from large to small was the more apparent. Mr. Holme
of Oxford mentions having taken Olisthopus rotundatus
in the Scilly Islands, in great profusion, none of the
specimens of which exceeded two lines and a half in
length. At Whitsand Bay in Cornwall I have captured
Gymnaétron Campanule, none of which exceeded three-
quarters of a line,—the usual length being from a line
to a line and three-quarters. Anthonomus ater, the
average length of which is two lines, I have taken a |

series of in Lundy Island, none of which exceeded one.

In the same locality, also, the common Ceutorhynchus
contractus scarcely ever reaches its natural size; and is,
moreover, so variable in colour, that I was long before I
could persuade myself that the species was not distinct.
Instead of the bluish-black elytra which I had always
considered invariable, they all possess a yellowish or
brassy tinge; and the legs, instead of being black, are in
most instances entirely of a light yellow,—and im all,

more or less inclined to that colour. I have received
from Mr. Hardy, of Gateshead, specimens of Haltica
rufipes*, captured by him on the coast, in which the
entire insect is of a uniform brownish-red hue. Of the
rare Mantura Chrysanthemi I have taken beautiful
varieties at Mount Edgcumbe and in Lundy Island,—
many of which inclined to a rich metallic-yellow, instead

of the brassy-brown of the ordinary specimens: also, in
the latter locality, particularly dark specimens of Tele-
phorus testaceus. In like manner, I might enumerate
other species equally remarkable; but T trust that those

* T perceive, on reference to the original examples, still in my
collection, that this was wrongly quoted as the Haltica rufipes. It
is the H. exoleta, Fabr., and it is thus entered in Messrs. Hardy and
Bold’s ‘ Catalogue of the Insects of Northumberland and Durham ;’
where they make the observation, “variable in colour; specimens |
from the sea-coast are frequently of a dark mahogany tint.” Ihave |
myself indeed, since I communicated the above remarks to the
‘ Zoologist,” taken its precise counterpart, in abundance, along the
Yorkshire coast, —from Bridlington to the extremity of Flamborough
Head; so that it may perhaps be regarded as a topographical state
which is more especially peculiar to the eastern shores of England,
north of the Humber.

already mentioned are sufficient to verify my observa-
tions, of the extreme liability to change which, more or
less, most insects possess when placed within the imme-
diate influence of the sea. How to account for it, I
know not. I mention it as a mere fact, and leave it for
others to assign a reason for its existence*.”
Apparently dependent, in a large measure, on the

same circumstance (namely proximity to the coast), the
Bembidium saxatile, Gyll., so common at the edges of
the mountain streams in the north of England, in Scot-
land, and throughout a portion of Ireland, presents itself
along our southern shores in the form of a permanent

|| variety; being, as the Rev. J. F. Dawson remarks, “more
| depressed, never narrower in front (the sides therefore
more parallel), whilst the colour is always much paler
and the spots larger,—that before the apex being round
and very conspicuous, and the anterior one occasionally
expanding over the surface very considerably+.” I have
taken it in profusion on the coasts of the Isle of Wight,
Dorsetshire, and Devon. And so with the Cistela sul-
phurea, Linn., which in certain maritime localities (as I
have particularly noticed on the sand-hills at Deal) is
liable to become so dark in colouring, that, without the
intermediate shades to judge from (which however may
usually be obtained in situ), it might stand a fair chance,
occasionally, of being mistaken for a separate species.
A Psylliodes in Lundy Island, allied to (if not identical

* Zoologist, iv. pp. 1283, 1284.
+ Geodephaga Britannica (London, 1854), p. 186.

with) the chrysocephala, Linn., found in abundance on
a Brassica along the ascent from the eastern landing-
place, varies “in every consecutive shade between the
limits of light yellow and dark metallic-green*,” the |
former of which states (the normal one on that rock) |
might have been fairly set down as specifically distinct \
from the latter, did not observation on the spot decide
the question for us without doubt.

Another curious example of the effect of local m-
fluences (amongst which proximity to the shore plays,
in all probability, an important part) on the external
aspect of insects exists in the Aphodius plagiatus, Linn.,
—which in this country is generally deep black. “ It is
a circumstance worth noticing,’ I remarked in the
‘Zoologist, in 1846, “ that the form which is looked
upon by the continental naturalists as the variety, is in |
England evidently the typical one,—for out of about |

sixty specimens which I captured [at Tenby in South /

Wales], only two possess the conspicuous red dashes on j
the elytra which are considered abroad as the almost
invariable accompaniment.” I have observed the same
peculiarity in the flat and damp spots between the sand-
hills at Deal, where I have never detected a single in-
dividual which is not perfectly dark; and I believe that
the greater number of the specimens which were ori-
ginally taken at Wisbeach, in Cambridgeshire, offered the
same geographical characteristics; whilst those which -
were found near the more inland towns of Peterborough \

* Zoologist, iii. p. 900.

and Norwich present a larger proportion of the ordinary
European state. The blood-red dashes, however, with
which the elytra of numerous insects are adorned, I have
constantly remarked possess a singular tendency to be-
come evanescent. It is indeed almost diagnostic of the
‘genus Gymnactron, either that its representatives should
| be thus ornamented typically, or else that those which
| are normally black should, when they vary, keep in view,
| as it were, this principle for their wanderers to subscribe
to. Thus, I have no doubt that the G. Veronice, Germ.,
is but a variety of the G. niger,—an opinion which T
expressed in the ‘Zoologist? nine years ago. Whilst
commenting on the Coleoptera of Dorsetshire, I then
stated, that “for my own part I must confess I should
have doubted the G. Veronice being really distinct from
the G. niger, for red dashes on the elytra seem naturally
peculiar, more or less, to the whole genus; and I should
therefore have suspected that, had occasional aberrations
from a black type existed (which is not unlikely), those
aberrations would probably assume a form which is so
common in the other species of the generic group*.”’
The Bembidium bistriatum, Dufts., is usually much
paler when found in saline districts (under which circum-
stances it was described as a distinct species by Mr.

Stephens) than when occurring in more inland positions,

The Blemus areolatus, Creutz., I have frequently re-

marked is similarly affected in brackish places: and I

think it far from improbable that the Stenolophus Skrim-
* Zoologist, v. p. 1941.

shiranus, Steph., is but a local modification (though not
altogether, perhaps, through marme influences) of the
S. Teutonus, Schr. The Dromius fasciatus, Gyll., not
being exclusively littoral, may be quoted as another case
in point,—the specimens which are collected near the
coast being for the most part singularly pale. In
speaking of the Anthicus bimaculatus, Illig., M. de la
Ferté observes: “ Il y a seulement lieu de remarquer que
les individus du bord de Vocéan sont généralement plus
pales que ceux des contrées orientales de P Europe, et que
ceux des côtes de France et de Belgique sont entièrement
dépourvus de tache discoidale*.” And bearing, in much
the same manner, on the subject of variations, the Anthi-

cus humilis, Germ., “ est une des espèces le plus générale-
ment répandues en Europe; mais il lui faut le voisinage
de Peau salée. Aussi on le rencontre non-seulement sur
les rivages de toutes les mers, méme de la Baltique, mais
encore aux bords des lacs salés, tels que celui de Manns-
feld, en Saxe. Ceux de cette dernière localité sont géné-
ralement noirs; ceux que j’ai pris à Perpignan sont d’un
rouge trés-clair, ce qui me porte a croire que cette espèce
est dans le méme cas que quelques autres Anthicus, dont
les variétés les plus foncées appartiennent au nord de
VP Europe, et les plus pales au midi t.”

Whilst touching on this immediate question of varia-

bility as dependent to a great extent, in numerous Cases,
on proximity to the sea, we may just notice the marked ten-

* Monographie des Anthicus (Paris, 1848), p. 149.
T Id. pp. 127, 128.

64:

, dency which even the insects peculiar to saline spots would
| seem in a large measure to possess, of converging, more or
' less obviously, to a lurid-testaceous, or pale brassy hue,

~\ in thei colouring. True it is that we cannot (as above

suggested) deduce any evidence of direct physical modi-
fications from amongst species which are strictly mari-
time, —seeing that we have no means of judging in such
instances whether similar phenomena would or would
not be produced in central districts also: nevertheless
we may perhaps detect in this general law some slight
indication of the effects which an atmosphere and soil
constantly impregnated with salt would be likely to
bring about in the external aspect of those members of
the insect tribes whose range is sufficiently extensive to
expose them to its operation. The bare mention of
such names as Nebria complanata and livida, Calathus
mollis, Pogonus luridipennis, Trechus lapidosus, Aépus
marinus and Robinii, Cillenum laterale, Bembidium scu-
tellare, ephippium and pallidipenne, Ochthebius marinus,
Psylliodes marcida, Phaleria cadaverina, Helops testa-
ceus, and Anthicus instabilis, so eminently characteristic
as they are of briny situations, will at once appeal to
our native entomologists; whilst the acknowledgement

of the same principle is no less conspicuous in a host
of other species which are not included in the British
fauna.

Hence, when we see the tendencies of coloration (not
to mention other particulars, often readily apparent)
essentially the same, both in insects which are peculiar

to, and in those which have overspread (from without)
certain regions or localities, it is impossible not to asso-
ciate some inherent controlling power with the regions
themselves; and we are driven to the conclusion, that
either well-defined races have been gradually shaped out,
by means of the physical influences to which they have
been exposed, or else that the species themselves (as
witnessed by the intermediate geographical links, which,
although sometimes rare, are in all instances to be found)
do assuredly merge into each other.

In addition to those which we have been just discuss-
ing, there are other influences (equally independent of
mere heat and cold) by which insect modifications may
be brought about,—modifications moreover of that pre- |
cise character which must be referred, in general terms,
to the nature of the country and of the soil in which |
they severally obtain : a very few examples, however, in
illustration of their action, must suffice for our present
purpose. The Tarus lineatus, Schonh., is slightly shorter
in Madeira, as also somewhat darker on its head and
prothoracic disk (and with its elytral striz less deeply
impressed), than it is in Algeria and Spain. The
Madeiran specimens of the Aphodius nitidulus, Fabr.,
are usually a little paler, and more distinctly punctu-

lated, than their northern analogues; as are also, in
the latter respect, those of the Clypeaster pusillus, Gyl.
The Scydmenus Helferi, Schaum, is permanently smaller
in the Madeiran group than it is in Sicily; and I
believe that the Achenium Hartungti, Heer, of those

islands, is but a local state of the A. depressum, Grav.,
of Central Europe. The Bembidium tabellatum and
Schmidtw, Woll., may be in reality but geographical
modifications of the B. tibiale and callosum of higher
latitudes; and the Malthodes Kiesenwetteri, Woll., of
the common European M. brevicollis. Calcareous deposits
would appear, ever and anon, to have considerable eff-
cacy in regulating the outward aspect of such species as
are able to adapt themselves to different geological
districts; and when in juxtaposition with the shore,
their effects are often very conspicuous. The Dromius
arenicola, Woll., is the Portosantan representative of
the D. obscuroguttatus, Dufts.; and distinct as it is in
colouring from that insect (as evinced both in Madeira
proper and throughont Europe), I believe it to be in
reality but a local condition of it, occasioned by a resi-
dence through a long series of ages on a calcareous soil.
For the same reason perhaps (though assisted, in all
probability, by the qualifying power of isolation), the
Hadrus illotus, Woll., may be specifically identical with
the Madeiran H. cinerascens. In like manner, the Bem-
bidium Atlanticum, Woll., which in Madeira proper is
frequently so dark that its elytral patches are sub-
obsolete, and which is but seldom brightly arrayed in
that island, assumes in Porto Santo (which is not only
more calcareous than the central mass; but is strongly
impregnated, as its streams and rills everywhere testify,
with muriate of soda) a permanently paler hue,—being
at times almost testaceous. Some districts seem to be

more prolific in varieties, generally, than others. The |

neighbourhood of Ipswich, in our own country, has
been cited by Mr. Curtis* as possessing this peculiarity ;
and I have remarked a similar tendency in certain parts |
of Ireland. The common Haliplus obliquus, indeed, of J
the Blackwater river, in the county of Cork, is usually
so dark and suffused in colouring, that it might be
almost taken for a distinct species, —its fasciæ, especially
the hinder ones, being occasionally evanescent.

One more example must satisfy us under this section,
—namely, the Harpalus vividus, Dej., of the Madeiran
group. So curiously is that insect affected by the
nature of the areas through which it successively as-
cends, and that too irrespectively of heat and cold (as
may be gathered from the fact that its phases on the
shore and upland heights are well nigh coincident), that
it may be appropriately singled out as a concluding in-
stance of the effects of those obscure local influences to
which we have been drawiug attention. “ Ranging
from the beach to the extreme summits of the loftiest
mountains, accommodating itself at one time to a low
barren rock of 20 yards circumference, at another to the
deep-wooded ravines of intermediate altitudes, around
which the clouds perpetually cling, and where vegeta-
tion and decay are ever rampant, or harbouring beneath
the rough basaltic blocks of the weather-beaten peaks
(6000 feet above the sea); we should naturally expect,

* Proceedings of the Entomological Society of London (Part 3.
New Series), p. 4.

à priori, to discover some slight modifications of out-
ward structure, according as the respective localities
differed in condition. And such we find to be every-
where the case. I am satisfied, moreover, that it is
only by a careful observation on the spot that an insect
like the present one can be properly understood; for, to
anybody acquainted with it practically in all its phases,
it is but too evident how many ‘species’ (so called)
might be established on undoubted varieties, where
there exists a desire for creating them, and where our
sole knowledge is gathered from a few stray specimens
collected by another person, and unaccompanied by local
information to render the aberrations intelligible. For
it must be tracked from the shore to an elevation of
more than 6000 feet before we are enabled to discern
the causes by which its development is controlled, or
even to connect by slow and easy gradations its opposite
extremes of form. And it is an interesting fact, that
the distance between its variations does not increase in
proportion to the distance between its altitudes. On
the contrary, it would seem to pass through its minimum
of size and maximum of sculpture at about the elevation
of from 8000 to 4000 feet; both above and below which,
—that is to say, as it recedes from the upper and lower
limits of the sylvan districts,—it becomes gradually
modified, and almost in a similar manner. Thus, to a
person who had visited Madeira and had picked up
specimens on the coast, and to another who had per-
chance penetrated into the interior, as passing visitors

ee ee ee EE

from the vessels are accustomed to do, and had brought
away examples from the wooded mountain-slopes, the
two insects would appear altogether distinct. For, com- l
mencing on the level of the beach, the usual type is
broad, flat, more or less opake, with the prothorax
almost impunctate, and the elytra soldered together.
. As we ascend higher, the breadth invariably diminishes,
the brightness, and depth of sculpture, seem (up to a
certain altitude) to increase, and the elytra are seldom,
or but very imperfectly united; until, on entering the
lower limits of the forest region, at an elevation per-
haps, ore rotundo, of 3000 feet, we find that it has
gradually put on a very different aspect,—being small,
narrow, bright, convex, comparatively ovate and deeply
striated; the legs and antennz have become exceedingly
pale ; the prothorax has altered considerably in shape,
being much narrowed behind and punctured; and the
elytra are nearly always free. In this state it continues

for about 1500 feet; when again emerging into the
broad daylight of the open hills, it recommences to
mould itself as it did below; until, having reached the
summits of the loftiest peaks, more than 6000 feet above
the sea, it has almost (though not entirely) assumed the
features which characterized it on the shores beneath*.”

* Insecta Maderensia, pp. 55, 56.

§ IV. Isolation ; and exposure to a stormy atmosphere.

Having in the preceding pages touched upon the sub-
ject of insect variability, as the occasional result, to a
greater or less extent, of climatal and other influences ;
let us now proceed to consider the importance of a
certain physical condition, which will be found, I believe,
on inquiry, to be accompanied by a more decided modi-
fying power than any which we have yet discussed.

Every one who has examined the natural history of
islands, both in theory and practice, must be aware of
the many difficulties which have constantly to be en-
countered, before the several phenomena can be satis-
_ factorily explained. Laying aside those forms which
| are manifestly endemic (the numerical proportion of
| which usually accords with the distance from the nearest
| mainland) “again and again are we baffled by the near
| resemblance of the various creatures to continental
| types —whilst the minute differences which they display,
from them, are at the same time so permanently fixed,
that we are almost precluded, under the ordinary ac-
ceptation of a “ species,” from regarding the two as un-
doubted descendants of a common stock: and thus it is
that insular faunas have frequently been magnified, in
the novelties which they are supposed to contain, far
beyond what is right. A person however who looks to
the causes of things, and is prepared to recognize effects
where there are fair grounds for anticipating them, will
not be slow to perceive, that, in the small deviations

71l

which we are so often accustomed under such circum-
stances to behold, the results of isolation itself (as an
active controlling principle) may be traced out; whilst
geology, ever ready to lend a helping hand when ap-
pealed to, will seldom fail to supply those intermediate
links of probability which the believer in specific centres
of creation must needs subscribe to, before he can draw
any deductions on a broad scale, or be competent to
analyse even the general bearings of a question thus
necessarily comprehensive.

Having thought it desirable to defer to a subsequent
chapter of this treatise the few geological reflections
which our subject may give rise to, it will not be my
aim to allude to them in the present section more than
is absolutely requisite. I propose rather to consider
some of the ordinary effects of isolation, as mere matters
of experience; and to allow geology to tell its own tale
when we come to examine the problem of self-dispersion,
as occasionally interrupted by subsidence.

If we except a few of the Heteromera and apterous
Curculionide, which appear to be influenced in a dif-
ferent manner, the power of isolation over insect form is |
perhaps more especially to be detected in a deterioration |
of stature. Whether this principally emanates from the
constant irritation of a stormy atmosphere, such as
small islands are of course exposed to, and which would
seem to have stunted the development (during a long
series of ages) of the animal and vegetable worlds, or

from a diminution of area consequent on the breaking

up of a continuous land, it is difficult to pronounce:
nevertheless, it is most consistent with both reason
and analogy to suppose that each of those causes has —
operated to induce a similar result; and that we must
thereforé,view them as working in concert, if we would
appreciate their action aright.

It is a law to which a large proportion of the organic
creation would appear to be subject, that the exuberance
of life (not so much, however, as regards the number of
individuals which the various species may present, as in

the grandeur of their size) has reference to the > magni-
tude of. the spot over which it is permitted. to range.

The unnatural breeding-in of a single race, which must
of necessity happen unless the intercourse with other
varieties of its kind be possible, has always been attended
with effects more or less pernicious; and in the Annu-
lose tribes I believe that the reduction of space which
geological convulsions have at various epochs brought
about, has been commonly succeeded (inter alia) by a
reduction of stature in those species which have been
cut off from their fellows. I do not assert that there are
no exceptions to this rule; for counter-influences may
at times prevail (as we shall shortly see), to neutralize
the above tendency. I hold it, however, as an absolute
truism, in physics, that a law without an exception is
an anomaly. If, therefore, we were once to admit the
latter to negative the former, no such thing as a law
could exist. Hence it follows, as a corollary (unless,
indeed, we are prepared to endorse that conclusion), that

where there is a law there must be an exception to it;

and that, consequently, exceptional cases, if not exceed-

ingly numerous, should never pervert our belief from an
otherwise presumptive truth.

This dwindling-down of size has seldom failed to
attract my attention, more or less, in almost every island
which I have hitherto had an opportunity of exploring:
space, however, will not permit me to dwell upon many
instances. I have already adverted to the diminished
stature of Anthonomus ater, Mshm, and Ceutorhynchus
contractus, Mshm, in Lundy Island,—the first of which
scarcely ever reaches, on that rock, more than half its
natural bulk. The late Mr. Holme, of Corpus Christi

College, Oxford, in like manner, captured the com- .
mon Calathus melanocephalus, Linn., and Olisthopus |
rotundatus, Payk., in Scilly,—the former of which |

seldom exceeded two lines, and the latter two and a
half, in length: and he also recorded, that the Bolito-
chara assimilis, Kby, is invariably smaller in those
islands than it is in the neighbourhood of Penzance *.
The Vanessa Callirhoé, Fabr. (a geographical analogue of
the Red Admiral Butterfly +, so common in our own

* Trans. of the Ent. Soc. of London, ii. pp. 59, 62.

+ Considering that the true Vanessa Atalanta, of more northern
latitudes, does occasionally occur around Funchal, it may be reason-
ably contended that the fact of its coexistence (on the same spot)
with the V. Callirhoé is strong presumptive proof that the latter is
a true species, and no climatal or insular modification of the former.
And so, judging from a distance, and without local evidence to ex-
plain this phenomenon, I should have concluded myself: never-

a MH

74:

| country), is permanently smaller in Porto Santo than it
is on the larger, more luxuriant and varied, and there-
fore more protected, island of Madeira proper. And, as
regards the Ptini of that group, so completely are some
of them “affected by isolation, and by exposure to a
perpetually stormy atmosphere, that they do not attam
half the bulk on many of the adjacent rocks that they
do in the more sheltered districts of the central mass ;
and so marvellously is this verified in a particular
| instance, that I have but little doubt that five or six
+ species (so called) might have been recorded out of one,
| had only a few stray specimens been brought home for
identification, without any regard having been paid to
the respective circumstances under which they were
found*.” That “one,” Protean, representative is the

theless, recollecting how easy of transport the larve and pup of
Lepidoptera necessarily are (of which we have the plainest assu-
rance in the almost certain introduction of the Pontia Brassice,
Sphine Convolvuli, Acherontia Atropos, &e. into those islands),
especially in a region which for more than a century has been
receiving a constant supply of vegetables and ornamental plants
from western Europe; I am induced to believe that the appearance
of the Atalanta is a comparatively recent one, whilst that of the
Callirhoé (which, unlike the typical Red Admiral, has naturalized
itself in nearly all portions of the group) must be referred to the
remote period when migrations over a long-lost continuous land
were in regular operation. The slowness of the change, in external
aspect, which the isolation of insects from geological causes would
seem to bring about (and which follows, as a corollary, if the above
conclusion be true), I propose to discuss in a subsequent chapter of
this work.
* Insecta Maderensia, p. 260.

“5

Ptinus albopictus, Woll.; and it is so eminently a case gi
in point, that it may be admissible to quote, in extenso,
a few of the observations which I have already pub-
lished concerning it :—

“The P. albopictus is the commonest of the Madeiran
Ptini, and by far the most variable, having a separate
radiating-form for almost every island of the group,—
whilst, at the same time, the whole are so intimately
connected together (and merge into each other) by
innumerable intermediate links, that it is impossible to
regard them, in spite of the opposite contour of the
extremes, in any other light than as different aspects of
a single species, according as circumstances may favour,
retard, or otherwise regulate its development. Insta-
bility in fact (in its broadest sense) may be considered
to be one of its most prominent characteristics, since it
appears to be more sensitive to isolation and altitude
than any of the other members of the genus with which
we have here to do,—as may be proved to a demonstra- |
~ tion by a careful study of its habits on the spot, where
the influences of position and exposure are, in nearly all
instances, more than sufficient to account for the suc-
cessive phases assumed. Thus, commencing with var. a,
which reaches its maximum in the sheltered ravines of
the central mass, the bulk is usually large, and the tints
comparatively intense. Var. 8. is likewise brightly
variegated, but it is smaller. Now, if our premises be
correct, that locality and the action of the external
elements have much to do with the changes in question,

we might have expected, à priori, that this state, from
its peculiarity to the Dezerta Grande, would not only
have reduced in dimensions (which it is), but in colour
also (which it is not). Here, therefore, observation, in
situ, becomes extremely important; since such does at
once convince us that its almost exclusive attachment to
the interior of the stalks of the Silybum Marianum,
Grtn. (the Holy Thistle of the ancients), with which the
more protected portions of that island everywhere
abound, affords it ample conditions, even on so bleak a
rock, for its completion. Nevertheless, its stature (as
uready stated) is slightly diminished in spite of this:
and when we come to examine the individuals which
infest the lichen of more open situations (aberrant how-
ever on the Dezerta Grande, and answering to the var. y.
of the diagnosis), we immediately perceive that both of
our required results are indicated, —the reduction not
being limited to size, but extended also to hue. In
Porto Santo this modification is the normal one,—where
the insect likewise displays the same lichenophagous
tendency, and where the districts in which it exists are
equally barren. But, if its maximum be attained in

Madeira proper, and a certain number of minor devia-
tions range throughout Porto Santo and the Dezerta
Grande, it still remains for us to show where its minimum
is to be obtained :—which, true to the modus operandi by
which we have conjectured its divers degrees of abortion
to have been brought about, would seem to be centred
on the Northern Dezerta, or Ilheo Chão. When we bear

in mind the minute dimensions of that flattened rock,
which does not include so much as a single valley, or

depression, within its bounds, and is consequently seldom
free from the violence of the winds (which sweep across
it incessantly, from whatever quarter they may arise); it
could hardly be supposed that an insect which is so obvi-
ously subservient to atmospheric control should not have
become materially affected, in its outward guise, through
long seclusion on such a spot :—and accordingly we are
not astonished to find the race which has been thus cut
off for ages on this extraordinary little island, itself as
extraordinary. It is indeed very remarkable to trace
out how clearly the agencies we are discussing have here
operated on the species under consideration,—for both
sexes (though especially the male) descend on the Ilheo
Chão to somewhat less than half a line in length, bemg
literally of scarcely greater magnitude than some of the
larger representatives of the Ptiliade |”*

I stated above, that, although this diminution of
stature is a very general accompaniment of isolation,
amongst insects which have been long cut off from the
rest of their kind, there is no rule without an exception
to it; and that, therefore, we must not always anticipate
the result which has been described. We should re-
member that immense periods of time are apparently
necessary before any perceptible change can come over
creatures from the stoppage of their migratory progress,
and the unnatural in-breeding of their several tribes ; so

* Insecta Maderensia, pp. 268, 269.

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that in islands geologically recent (which often implies,
however, their existence through epochs which would
sound vast indeed to ears unscientific) we must not in-
variably expect to discover evidences of this law. On
the contrary, we must first of all take into account the
age of their formation, before we can judge à priori as
to the probability of its operation through a sufficient
interval of time to have become conspicuous in its
effects. I say “through a sufficient interval of time,”
because the process of deterioration may be silently
going on, even now, in many an island, which has not yet
shown any matured traces of its action, except perhaps
in the case of a few species which appear to be more
particularly susceptible to contingencies from without.
We should then call to mind, that an enormous propor-
tion of nearly every insular fauna is composed of acci-
dental colonists during the last few centuries, in which
civilization and commerce have been unintentionally at
work in the cause of animal diffusion ; and that, there-
fore, if modifications in outward contour have not neces-
sarily resulted during a positive geological interval, it
would be absurd to look for them in the mere settlers
(as it were) of yesterday.

Thus, it will be perceived, how necessary it is to take
every element and contingency into account before we
venture to pronounce dogmatically on either the exist-
ence or non-existence of any physical law; and how
cautious we should be of denying the legitimate opera-
tion of external influences in one region, because they

would seem, primd facie, to be contradicted in another.

It is surely more philosophical to endeavour to reconcile
the two, by tracing out (as may frequently be done)
some opposing principle in the latter, which shall enable
us to understand the discrepancy, and to believe that
the same action may be going on in both cases, but that
in one of them it is either overruled by a greater con-
trolling power than itself, or else has not had sufficient
time to bring its fruits to maturity. If a proposition be
true, we should recollect that it is always so (under all
the circumstances and conditions to which it is appli-
cable) ; for, otherwise, it would be both true and false,— _
which is absurd: hence, ¿f my premises be true, that `
the general tendency of isolation is to diminish the
stature of those insects which have become isolated ; it
follows that that tendency must remain, so long as there
are no other special disturbing influences to absorb or
neutralize it. ‘‘ When any observation,” says a writer
of the last century, “hath hitherto constantly held true,
or hath most commonly proved to be so, it has by this
acquired an established credit: the cause may be pre-
sumed to retain its former force; and the effect may be
taken as probable, if in the example before us there doth
not appear something particular,—some reason for excep-
tion*2? Hence it is, that, even amongst the opposite
phenomena which one island may occasionally present
from those of another, I have often been able to recog-
nize the working of a selfsame law ; and clearly to detect,

* Religion of Nature Delineated, p. 99.

Same SE

that it is not from ifs failure, in either instance, that
contending results are brought about, but simply that
some counteracting agent has been exerting its energy
in the one case, so as to nullify what would have other-
wise come to pass.

The main object however of the present section being
to show that a considerable amount of power is due to
isolation itself, in regulating (after a long series of ages)
the outward aspect of the insect tribes, it is not strictly
necessary that we should so rigidly insist on deteriora-
tion of size as one of its primary consequences,—since

(whether it be so or not) we are merely concerned here
to demonstrate, that its influence, in some shape or other,
is absolute and real.

After the above remarks, we shall not be surprised
that the phenomena displayed in certain islands, as
regards size, are sometimes (though I believe it to be an

exception to the ordinary rule) the exact opposite of

what we have been describing. Let us not however be
alarmed at this fact, on the bare statement of it,—as
though the proposition which we have been lately ad-
vancing were at once disproved ; since we shall find, on
inquiry, that the case is not so desperate as might be
imagined; and that in many islands where even this
principle is to be detected, we may recognize traces of
the other also. But how, it will be asked, can this be?
for, since the influences are the same, creatures simi-
larly exposed to them must be similarly affected. Now,
although, on a broad scale, such a notion contains much

presumptive truth, on a narrower one it does not always
apply; for species are differently constituted ab ovo, and
will sometimes give a different result from the operation
of causes which are identical. Moreover, there is a
curious tendency which I have remarked in most islands,
that the wings (especially the metathoracic ones) of their
insect inhabitants are liable to be retarded in their
development,—often indeed to such an extent as to
become actually evanescent: and I believe it to be a law
of Nature, that when any particular organ is either |
stunted or taken away, the creature receives a compensa-
tion for its loss either by the undue enlargement of some
other one*, or else in a general increase of its bulk. If
such be the case, the presence of two apparently con-
flicting effects m a single island is rendered somewhat
more intelligible ; nevertheless, on the above hypothesis,
the specimens which increase in dimensions should un-
doubtedly have their organs of flight more or less en-
fecbled, whilst those which diminish should be regularly
winged. And hence we arrive at the question, is this

so? My own experience would certainly tend to prove

* Although the result of a primary (or creative) adjustment to
special circumstances, rather than of a secondary adaptation.
brought about by a self-modifymg capability ; we may just call
attention to the fact, that most of the blind insects, whether asso-
ciates within the nests of ants, or natives of subterranean caverns,
have either their palpi or antennæ anomalously developed,—as
though, partially (although how, and in what degree, we cannot
possibly ascertain), to make amends for the inconvenience which a
total want of sight must necessarily entail.

that it is; and I suspect that future observations will
confirm the fact. Meanwhile, I must content myself

with simply advancing the subject for consideration, and _
with recording such few examples, in support of the
theory, as space will permit, and which occur to me
almost spontaneously.

The Madeiras would seem to inherit, as it were, a
, more than usual control over the alary system of their
insect population ; for, out of about 550 species of Co-
leoptera which I have hitherto met with in that group,
nearly 200 are either altogether apterous, or else have
their organs of flight so imperfectly developed, that they
may be practically regarded as such; so that, if our
preceding conclusions (from the compensation-hypo-
thesis) be correct, we should à priori anticipate an in-
crease of bulk in those islands, rather than a decrease
of it. Unfortunately the greater number of these 200
representatives are now, through the submergence of the
once surrounding continent, endemic, so that we have
no means of judging whether the obsoleteness of their
wings is to be referred to the long action of Madeiran
influences*, or whether they were thus created severally

* This is certainly rendered probable, however, from the fact that
a large proportion of these apterous species are members of genera
which are usually winged,—such as Tarus, Loricera, Calathus,
Olisthopus, Argutor, Trechus, Hydrobius, Ephistemus, Syncalypta,
Phleophagus, Tychius, Longitarsus, Chrysomela, Scymnus, Cory-
lophus, Helops, and Othius,—whilst the knowledge that, out of
i twenty-nine genera which I believe to be endemic in those islands,
six only are winged (the remaining twenty-three being apterous),

in the beginning ; and, for the same reason (that is to
say, having no others of their kind to compare them
with), we cannot pronounce, even if we might assume
this partial organic decay to be the consequence of their
isolation on these rocks, whether their general stature
has been subsequently augmented or not. Still, there
are some few, out of the 200 just alluded to, which are
of common European distribution ; and, as these would

appear to have obeyed the principles to which we have
beeir calling attention, it is not unreasonable to suppose,
that-many of the others (could we but behold them as
they formerly were,—emigrants over a vast continuous
land) would be found to have done so also.

I alluded, in a previous section, to the Dromius
obscuroguttatus, Dutts., as presenting permanent charac-

teristics in Madeira,—the combined result of latitude
and isolation; and I also stated that it was not always
possible, whilst dealing with physical agents which are
necessarily obscure, to refer the respective phenomena
(whatsoever they may be), which would seem to have
departed from their types, to a single disturbing cause.
Hence, whilst I there acknowledged latitude as in part
answerable for the changes which that insect has under-
gone, I may here suggest that it is, in all probability,
to isolation that we must mainly look, if we would under-
stand those changes aright. But what are the distinctive
will not tend to diminish the probability that there is something

peculiar in the action of Madeiran influences generally on the alary
system of the insect tribes.

features, it may be asked, which the D. obscurcguttatus has
adopted, since its first arrival from more northern latitudes
over an unbroken* continent? It has not altered much,
after all: it is, however, the nature of the alterations,
and their constancy, which give them their real import-
» ance. In a few words then, the insect is rather larger
and more robust than its European analogue, and (to
omit other minor differences) its wings are evanescent.
But this, on our above hypothesis, is precisely what we
should have expected: for, since it is self-evident that
the species cannot have been naturalized accidentally on
these mountains, and since geology informs us that a
vast interval has elapsed since the Madeiran islands were

portions of a continuous whole, we have at once a suffi-

cient time assured us for the modifications to be com-
pleted, and to appear at length permanently adjusted in
accordance with the conditions and influences which
locally prevail.

There are other examples which might be quoted in
support of my theory,—that isolation, when involving a
sufficient period of time, has a direct tendency either to

* I do not think it necessary to apologize for the apparent dis-
posal of this questio vexata; because, from the wildness of the
upland ridges to which the D. obscuroguttatus is in Madeira ex-
clusively confined, I deem it an absolute impossibility that it could
ever have been introduced, through any chance agencies whatsoever.
And hence, unless we reject the doctrine of specific centres in toto,
I contend that it must have migrated, together with other insects
similarly circumstanced, by ordinary means, and without natural
impediments, from its own area of diffusion.

diminish the stature of the insect tribes, or else to neu- `^

tralize their power of flight ; but that, in the latter case,
the creatures, when thus despoiled of a function, do, on the
contrary (instead of deteriorating in size), often receive
a compensation for their loss by an actual increase in
their bulk. The common Bradycellus fulvus, Mshm, is
another instance in point. From its occurrence in the
almost inaccessible districts of the Madeiran group, far
removed from cultivation, I am inclined to refer its entry
into this southern region to that remote period when a
connective land offered a natural passage to wanderers
from the north. Hence our first stipulation, that of
sufficient time, is satisfied; and what is the result? The
insect is a trifle more robust than its ordinary European

representatives, and it is invariably apterous. The Ca- |
lathus fuscus, Fabr., is also, as is clear from its special

attachment to the mountain tops, strictly indigenous in
Madeira (that is to say, it must have arrived there
during the migratory epoch) ; and the consequence is,
that, although usually winged im our own country, it is
permanently subapterous in that island. I think it far
from unlikely that the Dromius negrita, Woll., may be
the ultimate phasis (from isolation) of the common D.
glabratus, Dufts..—from which it may be distinguished

by its somewhat larger bulk, more robust head and pro- |
thorax, and by the obsoleteness of its wings. True it is,
that the latter species flourishes alongside it in Madeira;
but, like the Vanessa Atalanta (when considered with
respect to the V. Callirhoé), may it not be of more recent

|
\
|

importation from the European continent, and as yet in
a transition state?—an idea which the smallness of its
wings, as compared with those of its British analogues,
would seem rather to corroborate.

But, if this slight increase of stature would appear
generally to accompany that gradual extinction of the
powers of flight which isolation is apt to induce, it
follows, on the other hand (as indeed I have lately
intimated), that where wings are so essential to the con-
tinuance of a species that they cannot, without its posi-
tive destruction, be taken from it, the primary effect of
isolation,—namely a diminution of bulk,—will for the
most part happen instead. As this fact, however, has
been already commented upon, we will not discuss it.
afresh.

Why it is, in the Insecta, that islands* should pre-
dispose to an apterous state more than continents, it is
not easy to speculate. Mr. Darwin has indeed suggested,
and with much apparent reason, that, were wings fully
developed, the indiscriminate use of them might lead to
unhappy results, by tempting the creatures to venture
too far from their native rocks ; and that, therefore, this
partial decay is, under such circumstances, a wise pro-
vision in their favour: whilst it has been urged, on the
other hand, that since insular species are at all times
liable during heavy gales to be blown out to sea, they

* Iam informed by Dr. Hooker, that the only two insects (belong-

ing respectively to the orders Coleoptera and Lepidoptera) which
he detected in Kerguelen’s Land were wingless.

should in reality be gifted with stronger powers of flight
(rather than weaker ones), to fortify them against such
disasters ; and that, consequently, the above phenomena
are not explicable on Mr. Darwin’s hypothesis. For my
own part, I am inclined to accept that theory, in all its
fullness ; and, furthermore, I do not believe that the latter
consideration (though it unquestionably contains much
presumptive truth) does at all interfere with the admission
of it,—seeing that either requirement may be fulfilled,
according to the nature of the several species which are
destined to be acted upon. Thus, if flight is absolutely
indispensable, as in the greater number of the Lepido-
-ptera, and beetles of a flower-infesting tendency, we shall
) find that the wings remain unaltered (if indeed they be
/ not actually increased in capacity, of which I am by no

means certain), and that the effect of isolation is more

particularly evident in a diminution of stature. But if,
on the contrary, the creatures are less dependent on
aérial progression for their sustenance, as in the pre-
dacious tribes generally, especially those of nocturnal
habits, the reduced area in which they are confined, in
conjunction, it may be, with the danger to which they
would constantly expose themselves by the promiscuous
employment of organs which their modes of life do not
positively need, would seem to render the presence of
wings unnecessary; and they are accordingly, by degrees,
removed :—in which case, however, a compensation for
the loss is not unfrequently granted by an increase (more
or less perceptible) in bulk.

In the Madeiras, this diminution and enlargement of
stature, accompanied for the most part respectively by
the retention and annihilation of the powers of flight, is
singularly traceable on the selfsame rocks, particularly
the smaller ones of the group. Thus, on the Flat
Deserta, or Ilheo Chão, the Scarites abbreviatus, Koll.,
Laparocerus morio, Schön., and the Helops Vulcanus,
Woll., attain a gigantic size; yetit is on that very island
that the Ptinus albopictus, Woll., finds its minimum of
development,—scarcely exceeding in dimensions some of
the larger members of the Trichopterygia. The Deserta
Grande has some special modifying capability of its
own,—the Lurygnathus Latreillei, Lap., Notiophilus ge-
minatus, Dej., Zargus pellucidus, Woll., Calathus com-
planatus, Koll., Olisthopus Maderensis, Woll., Caulotrupis
conicollis, Woll., Laparocerus morio, Schön., Omias Wa-
terhousei, Woll., Helops Vulcanus, Woll., and the Elllip-
sodes glabratus, Fab., being also larger on that rock
than is typical: all of them, however, with the excep-
tion of Notiophilus geminatus, are there, as elsewhere,
apterous. .

Other qualifying results, from isolation, are equally
apparent. Take colour, for instance; and we shall per-
ceive that in the Dromius sigma, Rossi, it is sensibly
affected. The normal state of that insect “does not
occur at all in Madeira proper, but only in Porto Santo.
True it is that the modifications in the several islands
present but slight differences inter se; nevertheless,
being constant, I would lay particular stress upon them,

since they go very materially to prove that the effects of

isolation on external insect form are even more import-
ant, if possible, than those of latitude. That this is
the case in the present instance, appears clear from facts
so minute as these. For, out of the many specimens
which have come under my observation from various
countries of Europe, if there is one point more constant
than another in this otherwise variable species, it is, 1
‘believe, under all circumstances, its immaculate pro-
thorax. Now, whilst this (we may almost say essential)
character obtains in Porto Santo, in Madeira it does
not hold good: the prothorax there is invariably infus-
cate in the centre; and on a small adjacent rock (the
Ilheo de Fora) it is entirely dark. Nor let anyone sup-
pose that details apparently so trivial are beneath our
notice, or the mere result of chance, since it is by the
observation of such-like points, and by marking their
development according to the circumstances of the
several localities in which they obtain, that we are alone
able to appreciate their importance, and so to form, in a
wider and geographical sense, a correct estimate of their
value*.” The Olisthopus Maderensis, Woll., is much
paler, larger, and more opake, on the Dezerta Grande
than it is in Madeira proper. So great indeed is the
change which it has undergone through a long isolation
on that rock, “that, had the case been a solitary one, I
should not have hesitated in regarding the specimens
obtained from thence as specifically distinct; neverthe-

* Insecta Maderensia, p. 6.

90 `

less, with the knowledge both of the modifying effects of
isolation, and also of the kind of modification essentially
peculiar to that island, I am perfectly satisfied that it is
a mere local state, although a very remarkable one, and
has no claim whatsoever to be otherwise considered *,”
The Pecteropus Maderensis, Woll., is of a greenish-
brassy tinge in Porto Santo, and much acuminated in
front; whereas on the Dezerta Grande it is almost
invariably coppery, and less narrowed anteriorly. The
Caulotrupis lucifugus, Woll., although ranging through
no very opposite phases, either of outline or sculpture,
“appears to possess a slight modification for every
island of the Madeiran Group: and hence small shades
of difference, which might otherwise be regarded as
trifling, become directly important, and cannot be
ignored in a local fauna,—even though a general col-
lector may deem it unnecessary to recognize them. In
real fact, however, such distinctions, when viewed geo-
graphically, are of the greatest interest, as serving to
illustrate what we have so often had occasion to com-
ment upon, namely the influence of isolation and other
circumstances on external insect formt? The Psyl-
liodes vehemens, Woll., is permanently paler in Porto
Santo than it is in Madeira proper, being almost entirely
testaceous. “That the species is identical, however,
with the Madeiran one I have not the slightest doubt,—
the sculpture and colour, as I conceive, having merely
undergone a change since the remote period of its isola-

* Insecta Maderensia, p. 36. + Id. p. 310.

tion on a comparatively calcareous soil*.” The Scarites
abbreviatus, Koll., occupies the loftiest peaks of nearly
all the Madeiran islands, and was probably once abun-
dant over the entire ancient continent, whatsoever its
limits may have been, of which the present group forms
but an isolated part. “There are traces of it in the
Canaries, from whence occasional specimens have been
brought, and which, from the want of local data and of
sufficient numbers to reason upon, have in their turn
been severally regarded as distinct. The fact however is,

that the species in question is an extremely variable one,

assuming differences of size according to the altitude at
which it lives, and differences of sculpture according to
the circumstances of the spot on which it is isolated.
That such is actually the case, a careful observation of
the many minute changes which the insect has under-
gone in the various islands and altitudes of the Madeiran
group will, I think, prove to a demonstration. For it is
impossible to suppose that every rock contains its own
species, that is to say, has had a separate creation ex-
pressly for itself, —a conclusion at which we must
assuredly arrive; if small and even constant differences
are of necessity specific. Rejecting therefore this hypo-
thesis as utterly untenable, and as contrary to all expe-
rience, we are driven to acknowledge that isolation does,
in nearly every instance, in the course of time, affect,
more or less sensibly, external insect form ;—which
being admitted, we have at once an intelligible principle

* Insecta Maderensia, p. 452.

whereby to account for modifications innumerable, each
of which, when viewed simply as a difference, indepen-
dently of the circumstances producing it, might have

been regarded as sufficient to erect a “species” upon,
had the desire for multiplying them overbalanced the
love of truth*.”

Such are a few of the circumstances, influences, and
conditions, by which the outward aspect of the insect
tribes is liable, within definite limits, to be more or less
regulated: and it is impossible to view them with an
unbiassed mind and not arrive at the conclusion, that
physical agents generally have a very decided control
over the external contour of these lower creatures, In
selecting the examples which we have lately discussed, I
have avoided as much as possible those startling in-
stances of variation which distant quarters of the globe
will readily supply, because there are vast numbers of our
naturalists who will not acknowledge the validity of any
evidence which would tend to amalgamate, in a broad
sense, the species of the Old and New Worlds. I have
therefore contented myself with such data as must fall
within our common experience, feeling satisfied that if
the principle be allowed in the one case, it cannot long
be objected to in the other. There are few entomolo.
gists who would not recognize, in the abstract, a legiti-
mate capacity for adaptation in every insect with which

* Insecta Maderensia, p. dls

they have to do; yet I believe there are not many, who,

if modifications were to be shown them as the fixed
result of disturbances from without, would be prepared
at once practically to accept them as such. The col-
lectors of the present day are so prone to regard every
permanent difference as a specific one, that a large pro-
portion of them do not sufficiently realize, that well-
marked races, or states, are no longer matters of hypo-
thesis, but of fact; and that, therefore, a sensible
amount of aberration should not only be conceded to the
action of certain physical combinations and elements,
but even anticipated and looked for. Such however
ought not to be; and earnestly therefore would I advo-
cate a greater latitude for geographical influences than
has been hitherto admitted by many of us. Especially
would I urge the necessity for a more careful study of
insular phenomena, for I am convinced that a due allow-
ance is seldom, if ever, made for the qualifying power of
isolation, per se,—the most significant perhaps of all the
conditions which we have attempted in the preceding
pages to examine.

“Felix qui potuit rerum cognoscere causas 7 is a
motto which the student of Nature should keep con-
stantly in view; for it is undoubtedly a more honourable
task to discover the reasons for what we see, than the
mere appearances themselves. He who has dived deeply
into the everyday circumstances around him will be
reluctant to ascribe so much as a single item of all that
comes within his ken, to chance; for to him the whole

system of created things is, from first to last, replete
with design. Natura nil agit sine causd is as true
now as it ever was, and it will be so to the end. Let us
not therefore be discouraged at the apparent smallness
of the data from which many of our conclusions have to
be drawn, for nothing is in reality trivial which is the
effect of a wisely appointed law; and, even were such
the case, it would not be thereby proved that the inves-
tigation of the law itself (however liable it may be to
exceptions) is unimportant. Nor ought we, on the other
hand, to be discouraged if we cannot always reconcile
conflicting phenomena, and detect in each a primary
controlling cause. We should rather bear in mind, that
the elements with which we have to deal are obscure,
and subject to permutations from which various results
must of necessity arise; and that it is only, therefore,
on a broad scale that we can look for uniformity of
action, even from conditions which may appear to be
identical. “ Nature is not irregular, or without method,
because there are some seeming deviations from the
common rule. These are generally the effects of that
influence which free agents, and various circumstances,
have upon natural productions*.” |

* Religion of Nature Delineated, p. 84.

CHAPTER IV.
ORGANS AND CHARACTERS OF VARIATION.

Havine in the preceding chapter briefly alluded to
some of the principal causes by which the outward
aspect of the insect tribes would seem to be in a large
measure (though within definite specific limits) regu-
lated, it may perhaps be desirable to gather into a
small compass, from those remarks, what the chief
organs and characters are which appear to be more
peculiarly beneath the control of the various influences
which we have been just discussing. To imagine that
when an insect has become much altered in its general
contour, all the parts of which it is composed are
equally affected, is contrary to experience; since obser-
vation warns us that there are but few actual members
which are capable of change,—whilst even the external
features, or secondary diagnostics, are only interfered
with according to a fixed law, the workings of which are
necessarily modified, in proportion as the constitutions

of the several animals are differently organized and
acted upon.

As regards positive structure, indeed, we can have
but few observations to communicate,—seeing that the
limbs and appendages themselves are usually of so con-

stant a nature, that disturbing agencies have little or no
power to divert them from their typical states. Still,
there are occasional facts on record, which would tend
to prove that even these are not altogether exempt from
the deranging force of certain contingencies from with-
out: the number of the antennal joints, for instance, in
the tribes where those organs are multiarticulate, is said
to vary; but how far this may be dependent on physical
influences, I am not in a position to decide. The con-
nateness of the elytra, again, is a character which we
may at any rate define as sub-structural; and this I
| have myself noticed, at times, to fluctuate, according to

| the circumstances and conditions of the respective

localities in which the particular species obtain. Such
is eminently the case with the universal Harpalus (the
H. vividus, Dej.) of the Madeiran Group. Speaking of
this peculiarity, in my volume on the Coleoptera of
those islands, I made the following remarks: “ But per-
haps its most singular character, and in which it differs
from every other Harpalus with which I am acquainted,
consists in the tendency of its elytra to become united
or soldered together. I say ‘the tendency,’ because
it is not always the case that they are joined (which,
since the law exists at all, is perhaps the more remark-
able), although in most instances, especially in localities
much exposed and but slightly elevated above the sea-
shore, they are. I have examples, however, from the
upper as well as the lower regions, in which both states
are represented ; and others again in which the elytra

are only partially connected, being free at the apex
though firmly attached towards the scutellum. In
every instance, however, even where they are united
throughout their entire length, a little force will succeed
in separating them, showing their structure, as I have

indicated in the diagnosis, to be sub-connate rather than
connate. But that it does require force to effect the dis-
junction, when they are really in the condition described,
is proved to a demonstration to any one who has seen

the remains of the insect beneath the slabs of stone on
many of the small adjacent islands where it most
abounds, or drifting about over the surface of the rocks,
—under which circumstances I have observed them in
immense numbers, apparently the accumulation of two
or three generations, which the violence of the elements
had not been able to sever. It is rare in the sylvan
districts to find them joined; nevertheless such is some-
times the case,—thus proving that the peculiarity is not
actually essential, but merely one which it is the ten-
dency of the species to assume, and which is more
developed in some specimens, and under certain condi-
tions, than in others.* ”

But by far the greatest amount of variability to which
insect structure is liable, is presented by the wings, — }
especially the metathoracic ones. The wings, indeed, i
unless I am much mistaken, are essentially (as compared
with other primary details) organs of variation, capable
of being more or less developed, according as the several

* Insecta Maderensia, pp. 56, 57.

countries in which the creatures are placed may necessi-
tate their action. I will not recapitulate the evidence
which I have already adduced, proving that islands have
an especial capability of their own, either for increasing
or neutralizing, as it may happen, the powers of flight
(in which latter case, however, a compensation is usually
made for the loss); but I will point to the data which
are there brought together, in support of the hypothesis
for which I am now pleading,—believing that they will
be found sufficient, on inquiry, to establish the doctrine
of alary mutability, so far at least as it 1s connected with
isolation as an element of control. If, however (irre-
spectively of its cause), the thing itself be recognized, the
principle is at once established ; and we may reason
upon it as a matter of fact. So that, if we can ensure
this concession or acknowledgment, the occasional
proneness to variation of these thoracic appendages is, as
a law, admitted. The only questions which would then
‘appear immediately to suggest themselves, are: Under

~ what circumstances do they principally fluctuate? and
-e why should it happen that organs which are apparently
| so necessary as a medium of subsistence, should be

` subject to inconstancy ?

Both of these have, in reality, been already replied to
in the preceding chapter. Nevertheless, we may briefly
(À repeat, that, so far as the first is concerned, it is in
> islands that we detect the maximum of instability to
which the wings of the Insecta are liable, and that it is
à in seasons of extraordinary heat that their development

is everywhere inclined (if at all) to be especially stimu-
lated: whilst, as regards the second, it will be sufficient
to state, that in continents, when any decided alteration
takes place in the organs of flight, it for the most part
comes to pass that an increased (rather than diminished)
action is the result; whereas in islands, provided that
the species are not absolutely dependent on aérial pro-
gression for their food (in which case, in order to
prepare for the contingency of being blown out to sea,
the capacity of the wings is commonly augmented), the
reverse is nearer the truth. So that the second problem,
—the reason why appendages thus apparently essential
should be subject to inconstancy,—is at once rendered
intelligible from the consideration, that it is only under
circumstances in which the indiscriminate employment
of those organs would be apt to bring the creatures into
trouble that (when not an actual sine quá non to their
existence) they are liable to be taken away; whilst, even
in that case, it generally happens that some partial equi-
valent for the privation incurred is granted, as a recom-
pense.

Mr. Westwood, in his admirable Introduction to the
Modern Classification of Insects, has recorded many
instances of alary variation; which, however, as he does
not appear to have noticed the peculiarity of island
faunas, are principally in corroboration of what I have
just insisted upon as the usual tendency in continents,
—namely, an enlargement of the erratic powers. Speak-
ing of the Aphelocheirus estivalis (a member of the

100

Hemiptera), he observes: “ My British specimens have
but short, rudimental, oval hemelytra, like those of the
bed-bug ; but I possess one of Bosc’s original examples,
described by Fabricius, not quite so large as the others,
in which the wings are fully developed. I do not, how-
ever, on that account, regard the former either as pup
or distinct species, but as undeveloped specimens in the
imago state*.” And whilst discussing the Hydro-
metride, he expresses himself thus: “ It appears to me,
that, from causes of which we are ignorant, numerous
individuals of many of the species of these tribes are
subjected to an inferior kind of development in the
imago state, which does not allow the acquirement
of wings,—which, however, in certain cases, acquire
their full size. Hence, I consider that the apterous
specimens of Hydrometra stagnorum, those with very
short elytra, and those with the full-sized wings and
wing-covers, are all in the imago state, although some
are more perfect than others+.” And, again, in his
reflections on the Hemiptera, Mr. Westwood says (and
most entomologists are aware of the fact): “ The species

of Gerris, Hydrometra, and Velia are mostly found per-
fectly apterous, though occasionally with full-sized wings.
Chorosoma miriforme, Prostemma gutiula, Pachymerus
brevipennis, &c., are generally found with very short
wing-covers, but sometimes with full-sized wings }.”
In like manner, the Cimex apterus, Linn. (one of the

* Introduction to the Modern Classification of Insects, ii. p. 466.
+ Id. ii. p. 469. { Id. ii. p. 454.

101

Lygeide) “ exhibits, in an eminent degree, the ordinary
occurrence of an imperfect perfect-state; whilst indi-
viduals are occasionally found with fully developed organs
of flight*”. Lyeus brevipennis, Lat., also ordinarily
occurs with abbreviated hemelytra; but it has been
found with them perfect by Westwood, as well as with
metathoracic wings.

None of the above examples however would appear to

do more than refer to the alary instability of the Insecta,
as a matter of fact; but this is all for which we are now
contending,—the preceding chapter having been in part
devoted to some of the presumptive causes of it. Whether

the specimens of Oncocephalus griseus, to which Spinola
called attention, were insular ones, I cannot say; but he
seems to have noted an example in which an opposite
phenomenon to those which Mr. Westwood has cited,
was displayed, and moreover to have speculated on the
conditions producing it, when he suggests: “ L’influence \
du climat septentrional parait avoir arrêté le développe- |

ment des organes du volt.” And, again, when com- |
menting upon the other tendency in a representative of \
the Reduviade, he says (‘ Essai,’ p. 96): “Je pense que )
la présence des ailes et leur développement dépendent |

du climat.’”? Whilst treating of two British species of
the same family, Mr. Westwood observes: “ The Pro-
stemma guttula, Fab., and Coranus subapterus, Curt., are
interesting on account of their being generally found in

* Introduction to the Modern Classification of Insects, ii. p. 480.
+ Essai, p. 103.

an undeveloped imago state,—the latter being either
entirely apterous or with the fore-wings rudimental,
although occasionally to be met with having the fore-
wings completely developed*.’” The common Phos-
phuga atrata of our own country has the organs of flight
very rudimentary, and much too small for use: yet the
late Mr. Holme of Oxford has mentioned, that he has
several times taken it on the wing, during the hot sun-
shine. And, concerning the Olisthopus rotundatus, he
states{ that every specimen which he captured in the
Scilly Islands was subapterous.

But facts like these are, after all, nothing more than
such as we may trace the counterpart of in higher ani-
mals than the Insecta. Mr. Gould informs me, that the
Swallows of Malta, which have but a comparatively
narrow space to cross over, to the African continent,
constitute (although specifically identical with them) a
distinct race from those of England,—all of which, he
believes, winter in Morocco. But, what are the differ-

EEE

ences displayed? From amongst many minor ones, of

a climatal or geographical nature, the most conspicuous
is the length of the wings,—those which have annually a
longer journey to perform having, through a course of
ages, acquired, as a race, a superior capacity for flight.
And, in answer to a late query on this subject, he adds
that all the sylvan birds in Malta, such as the Black-
caps, Willow-wrens, &c., though unquestionably of the

* Introduction to the Modern Classification of Insects, ii. p. 473.
——— + Trans. of the Ent. Soc. of London, ii. p. 60. | { Id. ii. p. 59.

103

same species as those of Great Britain, exhibit small
local characteristics by which they may be immediately |
distinguished,—such as the length of the wings, size of |
the bills, and tints of the plumage. So that the migra- |
tory birds generally, which pass to and fro between
Europe and Africa in that particular latitude, would appear
to form separate races from those which traverse the
ocean to our own country; and to be, most of them,

remarkable, inter alia, for a slight shortening of their

organs of transit.

If, however, the members of the insect tribes are
capable of but small variation in actual structure, with
the exception, in certain instances, of the greater or less
development of the wings; we shall find that their ex-
ternal characters are much more prone to instability.
There is not an item indeed of all their secondary
diagnostics which does not admit of a positive change;
and, though it be only within fixed limits that the
several modifications can occur, those boundaries are
frequently far apart, and include at times numerous
phases within their embrace which have been too often

looked upon as specific. Thus, whether we regard their `

bulk, outline, colour, or sculpture, anything like absolute
constancy, under all circumstances and conditions, doesnot
so much as exist; and we are driven to admit, that the
physical influences to which these various creatures are
exposed have a very decided power over their general
configuration and aspect. It would be needless, however,
to attempt to discuss the above details of aberration
separately ; because, where any one of them is especially

104:

interfered with, it usually happens that the others are
more or less involved with them: but we may offer a
few desultory remarks, which will tend to show that
disturbing agents are apt to mar them both individually
and as a whole,—and not only so, but to affect them in
a permanent manner (as indeed has been already inti-
mated), according as similar combinations of them are,
from local causes (as it were), selected, to be acted.
upon.

I have stated in the last section of the preceding
chapter that insect stature is eminently beneath the
control of contingences from without; adducing, amongst
other examples, in support of this, the Madeiran Ptinus
albopictus,—a species which, whilst it averages more
than a line in length on the central island of the group,
is reduced to less than half that bulk on a small and
weather-beaten rock (the Ilheo Chiao) at a distance from
it. Judging indeed from many hundred specimens of
the Ptini which I have submitted to a close comparison,
“the most constant of their characters would seem to be
outline and sculpture, whilst size and colour are appa-
rently the least to be depended upon :—so that trifling
differences may be of specific indication in the former
case, where in the latter much larger ones are worth-
less*.” I have in fact generally noticed, that size and
M colour are more peculiarly liable to be affected together.
| This, however, is nothing more than what we should
anticipate, since the same causes which have stunted the

* Insecta Maderensia, pp. 260, 261.

105

dimensions, during a long series of ages, of any par-
ticular creature, will for the most part be found to have
also impaired the brilliancy of its tints. Luxuriance of
vegetation and sheltered districts are alike conducive,
in the Annulosa, to the development both of the body
and its adornment; or, in other words, where the vege-
table creation attains its maximum (which it certainly
does not do in situations which are exposed to the irri-
tating consequences of a perpetually stormy atmosphere),
there the animal world will be usually observed to
thrive.

There are many insects which appear to have two
distinct states, both in magnitude and hue, which we are
seldom (in some instances, I believe, never) able to unite
by intermediate links, or grades; and yet which are
universally admitted, although found in actually the
self-same spots (a fact which prevents their being looked

upon. as separate, local modifications of a common type),

to be mere varieties of each other. They are, however,
exceptions to the general rule; and, although infringing
on the strict definition of a “ variety,” as given at a pre-
ceding page*, we nevertheless feel an à prior conviction
that they are by no means specifically dissimilar inter se.
Such phases, as regards stature, are presented by the
Brachinus crepitans and Lamprias chlorocephalus of our
own country ; whilst, as regards colour, the Philhydrus
melanocephalus, Aphodius plagiatus, and the Psylliodes
erythrocephala (constituting in its paler garb the P. ni-

* Vide supra, p. 5.
F5

106

gricollis, Mshm) may be quoted, as cases in point. Thus,
also, in Madeira, the Mycetoporus pronus, Erich., has a
large and small form, living in communion,—which I-
have never been able to connect, and yet which are un-
questionably identical (differing in no respect except in
size): and so have the Stenus Heeri, Woll., and the
Saprinus nitidulus, Fab.*

As regards the instability displayed by colour, in the
insect tribes, when subjected to the action of certain
conditions and influences from without, so much has
been said in the fourth section of the preceding chapter,

* Although, in our ignorance of their real nature, we cannot cite
them as actually analogous to these separate phases in certain
members of the Insecta, yet we are forcibly reminded by the latter
of the distinct states which many of the Terrestrial Mollusca pre-
sent (frequently in equal proportions) in the same localities. Thus,
ù most of the Pupe have at least two abruptly-marked forms,—a
\ larger and smaller one. Many of the Helices also exhibit this ten-
dency in an eminent degree: I have indeed been shown specimens
by Sir Charles Lyell of the Helix hirsuta, Say, from North America,
one state of which is considerably more than double the dimensions
of the other; and I believe it is a well-known fact that intermediate
links have not yet been observed to connect the extremes. May
not therefore the gigantic H. Lowei and Bowdichiana, which are
now extinct in the Madeira Islands, have been but forms of the
H. Portosanctana and punctulata, respectively,—co-existent with
them, though more sensitive to the great diminutions of altitude
and area which were consequent on the breaking-up of a once con-
tinuous land? If such be the case, however, it is certain that they
were far commoner at an early period than their smaller colleagues
(which, now, in their proper districts, absolutely teem),—seeing
that the latter are extremely rare in the fossil deposits, whilst they
themselves literally abound.

107

that it is unnecessary to repeat it here. True it is that
it was then my sole province to discuss the causes which
would appear to regulate, in a large measure, the external
aspect of the Annulosa ; yet the existence of inconstancy,
in the several organs and characters involved (with which
alone we are now concerned), was, by the nature of the
case, implied: so that if the disturbing element was de-
monstrated, the mere fact that the thing (whatsoever it
may have been) was interfered with, was surely proved.
à fortiori. I there pointed out the great proneness to
a change in hue which divers circumstances are apt to
induce; and I particularly instanced proximity to the
sea-shore, and other saline spots, as well as an attach-
ment to calcareous districts, as amongst the most power-
ful of the deranging contingences. In case, however,
that any further evidence should be looked for, on this
immediate subject, I will quote the followmg,—relating
to the Bembidium Atlanticum of the Madeira Islands,
which was but just touched upon in that chapter,—as a
concluding example of the general effect of physical
agents on the colour of these lower creatures. “Through-
out all the Madeiran Coleoptera there is perhaps no
insect which displays such an extraordinary range of
colouring as the present one does; and although it is
true that the section of Bembidium to which it belongs 1s
essentially a variable one, yet I am not acquainted with
any Peryphus in which the paler patches of the elytra
are so remarkably unstable, or which appear to be so
completely under the control of external circumstances,

a st
~ = N

108

as are those of the B. Atlanticum: and indeed unless

viewed in the mass, we should scarcely be inclined to
recognize the same species in the many aspects which it |

puts on between its extremes. The examination, how-
ever, of a very large number of examples, and a careful
consideration of the several localities and altitudes in
which they were taken, has convinced me that there is
unquestionably but a single type of form amongst my
entire series, since the whole are so intimately connected,
by successive gradations both of outline and colour, that
it is perfectly impossible to isolate even a single specimen,
or to draw a line of specific demarcation between any
two consecutive members of the chain. It will be per-
ceived, by a reference to the diagnosis, that the insect in
question passes imperceptibly from nearly a pure green,
through a well-defined spotted state, into one which has
the elytra almost testaceous,—the paler portions being
at last so largely developed as to become confluent, and
almost to cover the entire surface. In Madeira proper
the darker varieties would seem to be typical; whereas
in Porto Santo the brightly coloured ones preponderate,
and in fact are all but universal. Both extremes do
nevertheless occur in both islands, the tendency being
merely, in either case, to assume the particular modifi-
cation characteristic of the spot*.

And so it is with the outline and sculpture (no less
than with bulk and hue) : they also are equally liable to
disturbance from physical causes, as indeed has been

* Tnsecta Maderensia, p. 78.

109

already insisted upon. Like most of the minutiz of

variation, however, to which we have called attention, itis
more particularly on islands that this is to be observed,
—isolation, during an interval sufficiently long, appear-
ing to possess some especial control over the external
contour and surface of the insect races. Thus, in the
Madeiras, for instance, the Caulotropis lucifugus has its
prothorax more distinctly punctured, and its elytra more
perceptibly striated, in the principal island, than on any
of the smaller members of the group; in Porto Santo,
indeed, it is almost free from sculpture of any kind;
whilst its ally, the C. conicollis, apart from being some-
what larger, is, on the contrary, both more punctured
and striated on the Dezerta Grande than it is in Madeira
proper. The Omias Waterhouset, again (in addition to
its slightly increased bulk and less shining envelope, in
that locality), is more lightly impressed on the Dezerta
than it is in Madeira: and, not to mention other differ-
ences, the Ellipsodes glabratus is densely beset with
most minute granules on that same rock—whereas on
the mountain slopes of the central mass, it is highly
polished and glabrous. The Helops confertus, we have
intimated at a previous page, is less coarsely sculptured
in the lofty regions of Madeira, than in the lower ones:
and the H. futilis has its elytral tubercles apparent in
Madeira proper, but evanescent on the Dezerta Grande.
The Eurygnathus Latreillei assumes a permanent variety
on the Dezerta, the insect having become modified
through a long isolation on those weather-beaten heights,

110

—where it not only attams a more gigantic stature than
in Porto Santo, but is invariably also more parallel and
opake, has the sides of its prothorax more recurved, with
the punctures towards the lateral angles almost obsolete,
and the strie of its elytra somewhat ‘more evidently

punctate*.

Such examples, however, might be multiplied ad infi-
nitum; and I will not therefore devote further space to
the bringing together of facts which it is hardly possible
will be disputed,—especially as it has been my wish, in
the present chapter, merely to enwmerate what the organs
and characters principally are which are more peculiarly
sensitive to change, throughout the Annulose tribes.
This I may venture to hope, though briefly, I have in
part done; and I will consequently pass on to other
considerations, which, even if somewhat alien to the im-
mediate question of insect instability, should scarcely be
altogether omitted in a treatise like this.

* Insecta Maderensia, pp. 21, 22.

CHAPTER V.

GEOLOGICAL REFLECTIONS.

We frequently hear it asserted, that, since the members
of the Insecta are so numerous: and minute, when com-
pared with those of other departments of the organic
world, the entomologist, whose province it is to collect
and classify them, can have but little time, if he attempt
the real advancement of his particular science, for ge-
neralizations on a broad scale. Now, whilst there is
necessarily some reason in this remark (for the investiga-
tion of species is a work of such labour and drudgery
that it is apt to monopolize all the leisure hours which
the greater number of us are able to command), we
should recollect, on the other hand, that the soundest
theorists have ever been the most patient and accurate
observers ; and have, many of them, spent whole years
of their lives as humble students in Nature’s domain.
We need not be afraid that an occupation amongst
what is microscopically small is liable to cramp the
mind, and render it unfit for wider processes of induc-
tion, since the very opposite of this would seem to come
nearer to the truth. The understanding which has
been well tutored by a system of close and steady obser-

112

vation, which has been trained to seize upon differences
amongst the objects of our common experience, to
balance the importance of generic and specific charac-
ters, as tested in the acquisitions of our daily walks ;
and which has been gradually brightened and matured
by the habitual exercise of its judgment on the most
trifling phenomena around us, has usually gained strength
enough to form conclusions from such data, which will
not only stand the test of analysis, but will be free from
those eccentricities of genius which too often mar the
speculations of less practical naturalists. The mind,
moreover, having been chained and fettered for a season
to the mere detail of facts, breaks forth, under such cir-
cumstances, with all the vigour with which the contempla-
tion of truth has gifted it, and takes its flight as it were
to a clearer sky; and, though a reaction may at times
set in, hurrying it away into regions beyond its sphere,
it will assuredly return at length, fraught with the
soberness which its vocation has inspired, and commence
to build up its hypotheses, step by step, in harmony
with the material which it has amassed.

Yet though entomologists may be in reality as well
qualified as any other natural historians for drawing
general conclusions from the result of their researches,
it is impossible to conceal the fact, that, as a body, they
have not ordinarily done so. Whether this has hap-
pened through an accidental disinclination on their part
to occupy themselves in such matters, or (which is more

probable) from their whole time having been engrossed

113

by the dry routine of their science, I do not pretend to
determine: be the solution, however, what it may, the
inference is practically the same, —that the Annulosa
have not hitherto been sufficiently regarded, in the
great questions of zoological geography. But especially
have they been ignored during that most significant of
considerations which has been so ably brought forward
of late years by some of our keenest observers,—namely,
the distribution of animals, as affected by geological
changes, on the earth’s surface. .

It would be well if the collector of imsects would
devote at least a tithe of his energies to the speculative
branch of his subject. Certain it is that much would
probably be advanced, at first, on slender premises ; and
would, as a consequence, fall to the ground, leaving no
record behind it. Yet such must inevitably be the case,
at the outset, in every region of inquiry; and we are
prepared to expect it. It does not however follow that
good would not be developed also; whilst we are confi-
dent of the fact, that unless the trial be made, it cannot

possibly arise. No question has ever yet been mooted
without beneficial results: it has either been shown to be

absurd, and has received its death-blow on the spot, or
else truth has been elicited (indirectly perhaps), which has
at once shed a new ray of light on some of its obscurest
bearings. And so, assuredly, it would be in the present
instance. We cannot doubt that there is much to be
discovered in the past history of insect dissemination,
which would tend, when rightly interpreted, to explain

114

many of the occult phenomena of the present day ; and
we may be equally satisfied that this cannot by any

possibility be attempted without the assistance of geo-
logy. Let us therefore glance hastily at a few of those
more undeniable convulsions which we are aware have,
at various epochs, taken place; and endeavour to catch
a glimpse of how, in the common course of things, that
portion of the insect world would be affected which was
exposed to their influence.

First and foremost, perhaps, in importance, of all the
changes which it is self-evident have happened, may be
mentioned subsidence. Including, as it does, both the
general lowering of some countries, and the actual isola-
tion of others, there are, I believe, no physical crises to
which we could point, through the mstrumentality of
which the very ewistence of the insect races (not to
allude to their diffusion) has been, by the nature of the
case, more seriously interfered with. We know that
there are certain species of an alpine and boreal cha-
racter, which cannot live except in a climate of low tem-
perature,—guaranteed to them either by elevation in one
land, or by a higher latitude in another: and let us
picture the consequences of the gradual sinking of a
mountain chain, even to a small extent, the swmmits of
which only just afforded the conditions of atmosphere
necessary for the continuance of creatures like these.
Now this is an example by no means far-fetched, and
such as must have occurred in instances innumerable.
But, what would be the many results of a diminution in

115

the level of our imaginary range? It needs no argu-
ment to prove, that one at least would be manifest in
the total extinction of those forms which could not
adapt themselves to the increased heat. Others, which
were able with difficulty to endure the alteration, would
in all probability, even though they had now emigrated
to the loftiest peaks, flourish less vigorously than before ;
and it is not unlikely, moreover, that they would become
somewhat modified from their normal states,—states
which, be it recollected (for this is an instructive lesson),
would still exist in more northern zones. _

During my researches in mountain tracts, I have |
usually remarked, that the highest points of land either
teem with life, or else are perfectly barren. My own
experience would certainly tend to prove, that, in a
general sense, one or the other of these extremes does
almost constantlyobtain. And, although I would not wish
to dogmatize on phænomena which may in reality be ex-
plicable on other hypotheses, it would perhaps be worth
while to inquire whether the geological movements of
subsidence and elevation will not afford some clew to the
right interpretation of them. Be this, however, as it
may, I can answer, that in many countries, where there
are strong indications of the former, the alpine summits
harbour an insect population to a singular extent ; whilst
in others, where the latter is as distinctly traceable, the
upland ridges are comparatively untenanted. Now we
have already shown, that where the gradual lowering of
a region has taken place, there will be, of necessity, an

116

undue accumulation of life on its loftiest pinnacles,—
for, even allowing a certain number of Species (which
even formerly were only just able to find a sufficient alti-
tude for their development) to have perished, we shall
have concentrated at that single elevation the residue of
all those which have survived from the ancient elevations
above it. But, if, on the other hand, an area, already
peopled, be in parts greatly upheaved, there will be
either a universal dying-out, from the cold, of a large
proportion of its inhabitants, or else an instinctive
striving amongst them to desert the higher grounds on
which they have been lifted up, and to descend to their
normal altitudes: in both cases, however, the present

summits will display the same feature,—namely, utter

desolation.

Such are a few of the effects which elevation and
subsidence, even on a small scale, would seem (when -
tested by theory and practice) to produce. It yet
remains for us to suggest, that the latter, when carried
to its maximum, so as to cause the actual separation by
the sea of one district from another, is a contingency of
immense significance in regulating the distribution of
the Annulose tribes. Their outward contour and aspect
we have shown in a previous chapter to be very largely
beneath the control of isolation, provided a sufficient
time can be granted for the change: but their ultimate
absence from any particular place, through the impedi-
ment which it offers to their migratory progress, we
have not yet touched upon. Let us conceive, therefore,

117

an extensive continent; and, since the insects which at
present inhabit our earth must, if the doctrine of specific
centres be true, have been originally created in certain
definite spots, let us suppose a limited proportion of
them to have been first produced upon this tract. Self-
dissemination, we will assume, has been going on for
centuries: those species which were gifted with quick
diffusive powers have become pretty evenly dispersed
over its surface; whilst those of naturally slow or seden-
tary habits have peopled, comparatively, but small areas
around the respective localities of their birth. Such may
have been the case, at some fixed period, amongst the
aboriginal beings of any country which we choose to
select as an illustration. But there is another element
to be considered. If this region be not insular, it will
have received colonists from foci of radiation situated
beyond its bounds; and these, therefore, according to
their several capabilities for progression, will have, like-
wise, in parts, overspread, or tenanted, it. Now it is
impossible to cite a more simple example than this.
But let us endeavour to realize what would be the neces-
sary consequence of the breaking up of such a district as

that which we have imagined. Ifa general sinking should

take place, causing its higher points to be alone visible
above the ocean, or merely a partial one, so as to admit of
the sea encompassing portions of it which would remain
unaffected in their altitude; the result practically would be
the same,—namely, the constitution of a group of islands
out of a once continuous land. Then, as regards the

118

animal population of this tract, the main phenomena are
almost self-evident. Should any of its isolated frag-
ments chance to contain a portion of one of those limited
areas which a species of slow progressive powers had
succeeded in colonizing, it would of course harbour (pro-
vided that the other portion has disappeared) what would
now be defined as endemic. Numbers of these small
areas, or, in other words, of the species which had over-
spread them, would in all probability be lost for ever ;
whilst the occurrence of any of the surviving ones in
more than a single island would manifestly depend on
the proximity of the islands inter se. Those forms which
‘had diffused themselves over the whole original con-
tinent would now be found in all the detachments of the
cluster; whilst others, which had wandered over the
greater portion of it only, might be traceable perhaps in
every island except a few.

Such are the primary facts which suggest themselves,
whilst discussing the question of isolation as regulating
the distribution of the Annulose tribes. Its after effects,
on their external configuration and development, we
have examined in a preceding chapter of this treatise ;
and we have also lately intimated what might be a few
of the presumptive consequences of a subsidence (in a
general sense), apart from the still more important
principle of isolation. Before, however, we dismiss these
brief and elementary reflexions on the upward and down-
ward movements which geology testifies to have occurred,
at various epochs, on the earth’s surface, I shall per- `

119

haps be pardoned if I digress so far from my immediate
subject as to trace out some of the actual results of iso-
lation in the diffusion of the Insecta (especially recogni-
zable in the stoppage of a former migratory progress) in
a few of the northern Atlantic groups. I should pre-
mise, however, that it is from the Coleoptera alone that
I shall attempt to draw my inferences; nevertheless,
since that order is more extensive than any of the others,
and has moreover been closely investigated in most of
those islands, it may possibly afford us data of sufficient
comprehensiveness and accuracy for practical purposes.
To commence, then, with the Madeiras and Canaries ;
the first facts which isolation discloses to us, concerning
the statistics of a region which was once continuous
throughout that portion of the Atlantic, are the slowness
and the direction of the ancient migratory movements.
The former of these is rendered evident from the vast
number of endemic species which are at present con-
tained, not merely in the two groups combined, but in
the several islands of which each of them is composed.
True it is, that these peculiar forms are, most of them,
apterous, and of naturally sluggish self-disseminating
powers ; yet, still the circumstance remains, that these
various creatures had not overrun areas of any extent
before the land of passage was destroyed,—for otherwise
they must have occurred, now, on islands and rocks but
slightly removed from each other, which they do not.
The latter of the above conclusions, namely, the direction
of the migratory current, will become apparent in the

120

sequel. We may premise however, that, so far as the
aborigines of this province are concerned, their course
will be found, upon the whole, to have been a northerly
one.

As regards the slowness, and the direction, of the
quondam migration (questions which can scarcely be
treated apart from each other), some light may be
thrown on the subject from considerations like the fol-
lowing. The Canaries are the head-quarters of the
genus Hegeter ; Teneriffe may indeed be called the land
of Hegeters. No less than thirteen or fourteen species
have been recorded as indigenous to those islands ; and
there can be no reasonable doubt whatsoever that that
ancient region (when continuous and entire) was the
primeval centre, or range, of that Heteromerous group.
The Hegeters are an apterous race, and of a sedentary
temperament ; hence, when the area (whether by general -
or partial subsidence, it signifies not) was broken up, it
is not surprising that those local fragments of it should
have become the nucleus of reception, as it were, for the
members of that genus. Nevertheless, a few of these
many representatives (of more discursive capabilities per-
haps than the rest) had found their way, before the
period of dissolution, to a considerable distance from
their original haunts. Thus, one of them (the H. late-
bricola, Woll.) had arrived at what now constitutes the
rocks of the Salvages; another (the H. elongatus, Oliv.),
at least, if not two, had colonized the Madeiras, and is
said (though I believe incorrectly) to have even reached

121

the present coast of Portugal. This latter species is
clearly of a more adaptive nature than its allies, inas-
much as it has, also, naturalized itself (though this may
be a more recent, and accidental, circumstance) on the
opposite shores of Africa. One thing, however, is at any
rate manifest,—that the Hegeters attain their maximum
in the Canaries, and that a few members only have been
sent off, in a northerly, or north-easterly, direction,
from thence.

In like manner, the genus Tarphius is distinctively
Madeiran. I have detected nearly twenty well-defined
species of it in that group; yet, out of so large a
number, two only have occurred beyond the central
island. Now the Tarphii are, also, wingless; and crea-
tures of very sluggish propensities,—scarcely ever stir-
ring from the masses of loose rotting timber which they
so assimilate in hue, and to the under sides of which
they affix themselves, day and night. Although difficult
to investigate in their precise economy, it is extremely
probable (may I not say, certain ?) that some important
and peculiar office is assigned to them in the remote
upland districts to which they exclusively belong: and
there cannot be any question, to a person who has
Studied them carefully on the spot, but that the region
which they now inhabit is the actual area of their prim-
eeval appearance on this earth. Many kindred species
may of course have been lost, during those gigantic
subsidences which caused the Madeiras to be shaped

out, and to tell their tale above the waves as ruins of an
G

122

ancient land ; yet our existing cluster of forms could not
have wandered far at that early period, from the Serras
and ridges of their birth,—perhaps not so far indeed
(considering the limited bounds within which they are
now confined, and that time should in reality have
increased their range rather than diminished it) as they
have succeeded in doing at the present day. Hence
we may reasonably conclude, that Madeira proper is an
example of what we have alluded to in a preceding page,
—namely, of the accidental retention, during a vast

downward movement, of a nucleus of small specific areas
of colonization, the colonizers of which had not extended
elsewhere. But I stated, that two of the above-men-
tioned Tarphit have occurred beyond the central mass.
It is in Porto Santo that they make their appearance ;

nevertheless, since one of them is apparently peculiar to
that island, it is only the T. Lowei, Woll. (an insect of a
different, and more active, nature than the rest) which
/ has violated that local eaclusiveness which would seem to
\ be almost a generic character, as it were, of its allies.
‘That species, however, both in its manners and aspect,
recedes materially from the remainder. Although, like
them, nocturnal in its habits, it is able to run with con-
siderable velocity ; and, instead of attaching itself to the
blocks of putrefying wood, which both fall and decay in
situ on those elevated tracts, it hides within the bunches
of Evernia scopulorum and prunastri which clothe the
trunks of living trees, and fill up the crevices of the
weather-beaten peaks. Hence, when contrasted with

123

its comrades, we can easily understand how the varied
processes of accidental transportation would operate to
increase the range of a creature which differs so essen-
tially, in many respects, from them. It is indeed, not
unfrequently, brought down, at the present day, by
human agencies from the mountain-slopes; for, since
the cutting of faggots is one of the few sources of live-
lihood to a large proportion of the poor of Funchal,
numerous insects of subcortical and lichen-infesting
tendencies are subject to be naturalized (provided they
can adapt themselves to the change) in altitudes lower
than their normal ones : so that there are many chances,
even à priori, in favour of the T. Lowet having over-
spread, whether by natural or artificial means, a wider
area than its congeners. I believe that there is no such
thing as a Tarphius in the Canarian Group: neverthe-
less, singularly enough, a representative, which is more
akin to the T. Lowei than to any other hitherto dis-
covered (and which was imagined until lately to have
been the sole exponent of the genus), namely, the
T. gibbulus, Germ., occurs in Sicily. From which data
we arrive at this significant fact: that, whilst Madeira
proper is, without doubt, the original centre of the
Tarphii, two species (one of which is, likewise, Ma-
deiran) are found in Porto Santo, to the north-east of it ;
whilst a third makes its appearance in an island of the
Mediterranean.

The genus Acalles presents a nucleus of species in the
Canaries, moulded on a very large pattern. A closely

124

allied member, the 4. Neptunus, Woll. (which may per-
haps be in reality but an insular modification of the
A. argillosus, Schön., from Teneriffe), has been detected.
on the rocks of the Salvages, to the north of them;
whilst on the Dezerta Grande, one of the most southern
_ stations of the Madeiran Group, we have a third, which
displays far more in common with the Canarian type
than it does with that which obtains in Madeira proper ;
| —which last is gradually, in its turn, merged into the
ordinary European form, The genus Pecteropus, Woll.,
is another instance in pomt. I possess three or four
species from the Grand Canary, Fuertaventura, and
Teneriffe ; and I believe it will be found, on inquiry, to
attain its maximum in that cluster. Unlike the others,
however, which we have just cited, it 1s powerfully
winged ; and we should consequently expect to trace the
evidences of its northward progression with comparative ©
perspicuity. Can we therefore do so? Yes: in Ma-
deira proper it has two representatives, and m Porto
Santo (to the north of it) one. And so with Xenostron-
gylus, Woll. (which is likewise winged), we have two
species, at least, in the Canaries; one in the Madeiras ;
and a third, unless I am mistaken, in Sicily. The genus
Ditylus is shadowed forth in the Canary Islands by two

or three singular representatives of a pallid, testaceous
hue; and, although the group is entirely absent in Ma-
deira, a species (the D. fulvus, Woll.) is found on the
‘Great Piton’ of the Salvages, so nearly resembling,
except in its smaller size, one of those from the Canaries

125

that I think it far from improbable that it is a fixed
insular state of that insect. Deucalion, also, may be
quoted in support of this twofold hypothesis, of the
direction, and the slowness, of the former migratory
movements. It is an apterous genus, and of eminently
sluggish habits ; and what is the consequence ?—we have
a very remarkable species (the D. oceanicum, Woll.) on
one of the rocks of the Salvages, whilst another (the
=D. Desertarum, Woll.) has been isolated on the two
southernmost islands of the Madeiran Group; and of so —
sedentary a nature is this last, that, although physically j

|| unimpeded, it has not, even to this day, overrun the

\\ diminutive areas on which, when the surrounding region
\\ was submerged, it was originally saved from destruction.
So strongly indeed was this fact impressed upon me,
when I first detected it, that I shall perhaps be excused
for recapitulating in extenso the few reflexions which
then suggested themselves to my mind. “There is no
genus, perhaps, throughout all the Madeiran Coleoptera,
more truly indigenous than Deucalion. Confined appa-
rently, so far as these islands are concerned, to the
remote and almost inaccessible ridges of the two south-
ern Dezertas, it would seem to bid defiance to the most
enthusiastic adventurer who would scale those dangerous
heights. Its excessive rarity, moreover, even when the

localities are attained, must ever impart to it a peculiar
value in the eyes of a naturalist ; whilst its anomalous
structure and sedentary* mode of life give it an addi-

* “ When we consider indeed the apterous nature of Deucalion,

126

tional interest in connexion with that ancient continent,
of which these ocean ruins, on which for so many ages it
has been cut off, are the undoubted witnesses. Approxi-
mating in affinity to Parmena and Dorcadion, yet pre-
senting a modification essentially its own, it becomes

doubly important in a geographical point of view; and

it was therefore with the greater pleasure that I lately
received a second representative, from the distant rocks
of the Salvages,—midway between Madeira and the
Canaries. Differing widely im specific minutiz, yet
agreeing to an identity in everything generic, they offer
conjointly the strongest presumptive evidence to the
quondam existence of many subsidiary links (long since
lost, and radiating in all probability from some interme-
diate type) during the period when the whole of these
islands were portions, and perhaps very elevated ones, of
a vast continuous land. x k k x * The Deucalion-
Desertarum is of the utmost rarity, the only two* speci-

its subconnate elytra, and its attachment (at any rate in the larva
state) to the interior of the stems of particular, local plants, or its
retiring propensities within the crevices of rocks; we are at once
struck with the conviction, that, during the enormous interval of
time which has elapsed since the mighty convulsions which rent
asunder these regions terminated, it has probably never removed
many yards from the weather-beaten ledges which it now inhabits.”

* Since the above was published, I have succeeded in detecting
one more example,—namely (in June 1855) on the summit of the
Ilheo Bugio, or Southern Dezerta, within a few yards of the self-
same spot where it was found by the Rev. R. T. Lowe in May 1850.
Although I searched diligently on the Dezerta Grande, during my
late campaign in the Madeira Islands, I was not able (so great is
its rarity) to discover farther traces of it on that rock.

127

mens which I have seen having been captured (the first
by myself, in 1849 ; and the second by the Rev. R. T
Lowe, in 1850) on the respective summits of the Middle
and Southern Dezertas. So local indeed does it seem to
be, that it, apparently, has not extended itself even over
the Dezerta Grande (where there are no external ob-
stacles to bar its progress); but retains the very position
which in all probability constituted its original centre of
dissemination at the remote period of time when this

ancient continent received its allotted forms. Judging
from the slowness with which creatures of such habits
must necessarily, under any circumstances, be diffused,
it is at least unlikely that the present one could have
circulated far, when the now submerged portions of that
region began to give way; and hence it is not impossible

that the Southern Dezerta, with the adjacent part (then
united to it) of the Central one, may have embraced the
whole area of its actual primeval range,—the remains
of which (though they be now separated by a channel) it
still continues to occupy, and from which, even when
physically unimpeded, it has never roamed*.”

Although it is not my province in this volume to draw
inferences from data which are not strictly entomologi-
cal, I shall perhaps be pardoned. for adding a few words
on the testimony which the Land Mollusca of the
Madeiras would seem to afford, in support of the general
slowness of the animal migrations over that primeeval
continent. The researches of the Rev. R. T. Lowe, and

* Insecta Maderensia, p. 435.

128

of myself, on every rock and island of the group, have,
it appears, so nearly exhausted the whole number of
species which lately remained to be found, that the con-
chological statistics are perhaps, at the present time,
more accurate than those of any other department of the
fauna: and, independently of the modifications which
have been manifestly brought about, in some few instances,
by isolation, since the periods of subsidence, it is truly
singular to remark how every detached portion of the
entire cluster harbours real species, which are now pecu-
| larly its own. Thus (to select an illustration from
|; amongst the most anomalous of the endemic forms), we
|| have in Madeira proper, Porto Santo, and on the South-
| ern Dezerta, respectively, true representatives, in the
| Helix tiarella, coronata, and coronula,—which in all
| probability still occupy the positions (or nearly so) of
their original début upon this earth. Considering the
sluggish, or sedentary, nature of the Terrestrial Mollusks,
it is extremely likely (nay, almost certain) that many
mtermediate links, radiating from the same type, were
lost for ever, when the gigantic movements which rent
this ancient region were in course of operation : so that,
if such were in reality the case, we need not be surprised
that one at least of this small geographical nucleus should
have been preserved on three of the existing islands of
the group. That these are actual species (saved alive
from their fellows, after the wholesale destructions in
_this Atlantic province had been completed), and no
results of insular development, is demonstrated by the

129

fact that two of them (for the third has apparently
become extinct) have not altered one iota since the fossil
period, which, in the opinion of Sir Charles Lyell, is
anterior to the dissolution of the intermediate land ;—
whereas, had they been mere modifications of each other,
induced by the local conditions and influences to which
they have been, through a long series of ages, severally |
exposed, the difference between their recent contour and
that of their fossil homologues would have been doubtless
at once conspicuous. I gather, therefore, that like the
Tarphii, to which we have lately drawn attention, they
are veritable surviving members of an esoteric assemblage
which found its birth-place on this post-miocene (?) tract.

In a similar manner, the H. undata in Madeira pro- \
per, the H. Vulcania on the Dezertas, and the H. Porto-
sanctana in Porto Santo, are representative species,— J
each occupying the same position, and being equally
abundant, on their respective islands: and, although it
may be a problem whether the second of these is not an
insular modification of the first (or vice versd) ; yet, with
the analogy of the three already mentioned before us, I
am inclined à priori to view it as distinct. These, also,
occur in a subfossil state; and no alter ation appears to
have been brought about, by either circumstances or
time. And so itis with numerous others (as the H. latens
in Madeira, and the H. obtecta in Porto Santo; the
H. squalida in Madeira, and the H. depauperata im
Porto Santo; the H. Delphinula in Madeira, and the

H. tectiformis in Porto Santo), which are no less repre-
G5

130

sentative inter se. From which we are driven to con-
clude ;—first, that this quondam continent was densely
stocked at the beginning with foci of radiation created
expressly for itself* ; and, secondly, that the areas which
these various creatures had overspread, before the land
of passage was broken up, was extremely limited,—or,
which amounts to the same thing, that their migratory
progress was unusually slow.

Touching the two-fold question, of the local engage-
ment of this Atlantic district with specific centres of
diffusion, and the extreme slowness of their diffusive pro-
gress, much instruction may be derived from a contem-

plation of the conchological statistics. Porto Santo, for
instance, is a very small island (not more than seven
miles in length), yet the number of endemic species
which it includes is so perfectly astounding that it may
be appropriately termed a generic area of radiation.

* It would seem, when viewed on a broad scale, as if particular
districts throughout the world had been made as it were the special
fields for the exercise of the creative force,—or that, generic areas
of radiation were part of the elementary design. Thus, Professor
E. Forbes records his belief that most, if not indeed all, of the ter-
restrial animals and plants now inhabiting Britain are members of
specific centres beyond its bounds,—they having migrated to it over
a continuous land, before, during, or after the glacial epoch. Hence,
since the greater number of them are supposed to have come from
the central Germanic plains, we may assume that those plains were
one of the primary areas of diffusion for a large mass of created
beings. There is guod cause for suspecting that the Pyrenean
region may have been another; and certainly all evidence would
tend to prove that this vast Atlantic province was, also, well stocked
with aboriginal forms.

131

Nor does this primæval excess of its aboriginal beings

strike us more forcibly than does the utter quiescence
(if I may so express it) which has been going on amongst
them. since the remote era of their birth. Although a
few have apparently died out* since that epoch, conse-
quent perhaps on the change of level and diminished

range which took place during the process of subsidence; , ,

we are amazed to find that certain species which are now

limited to particular spots (even whilst unopposed by | a

physical barriers) have been absolutely peculiar to them ' |

* Assuming the Helix Lowet and Bowdichiana to be gigantic
phases of the H. Portosanctana and punctulata, respectively; four
only, namely H. fluctuosa and lapicida, Achatina Eulina, and Cyclo-
stoma lucidum (the first three of which are extinct throughout the
entire group), seem to have altogether disappeared. Nevertheless,
the gradual dying-out, as it were, of species, both here and in
Madeira proper, is singularly evident. Thus, in the latter, the Cani-
cal beds show the H. tiarella to have been once most abundant (it
literally teems in those calcareous formations). Yet so rare is it in
a recent state, that, until the summer of 1855, when it was detected
by myself and the Rev. R. T. Lowe in two remote spots along the
perpendicular cliffs of the northern coast, it was supposed to have
been lost for ages. And the same may be said of its counterpart,
the H. coronata, in Porto Santo,—which, likewise, swarms im every
fossil-bed of that island; but which was, also, until I met with it,
on the 15th of December 1848, adhering to slabs of stone at a con-
siderable depth beneath the ground, on the extreme eastern peak
(opposite to the Ilheo de Cima), imagined to have long passed
away. And so, reasoning from analogy, I think it far from impro-
bable that the third representative of this little geographical assem-
blage,—the H. coronula of the Bugio (which has hitherto only
occurred in the mud deposits on the summit of that rock),—may be
still alive, though perhaps in very small numbers, on some of the.
inaccessible ridges of those dangerous heights.

tat fromm

182

from the first,—or, in other words, that, whilst the fossil
deposits extend throughout the lower regions of the |
island, far and wide, it is only in those respective por-
tions of the beds which join on to the present “ habitats ”
that the fossil homologues of several of the species are
to be met with. The H. Wollastoni is eminently a case
in point. That most interesting of the Madeiran Mol-
lusks was first detected by myself on the southern ascent
of the Pico de Conseilho, of Porto Santo, April 22, 1849 ;
and the subsequent explorations of the Rev. R. T. Lowe,
in conjunction with my own, have, I think, satisfactorily
proved that it occurs nowhere else except upon that
single slope. Throughout the large expanse of calcare-
ous incrustations which are spread over the island else-
where, and on the adjoining Ilheo de Baixo, all of which
teem with shells, I think I may assert, without fear of
contradiction, that the H. Wollastoni does not so much
as exist. Yet at the Zimbral d’Areia, which the Pico de
Conseilho directly overhangs,—a rich tract for these
fossil remains,—as well as in the muddy composition of
a cliff near at hand, it literally abounds. |

` In like manner, we might recall many others which
are peculiar, recent and fossil, to the self-same precincts.
Such, for example, are the H. calculus and commizta,
which swarm on the summit of the Ilheo de Baixo, in
both states. The H. attrita, again, is the Pico d@’Anna
Ferreira modification of the H. polymorpha; and it is
only in the beds towards the base of that mountain that
its fossil homologue is found. But what do these facts

133

indicate? Surely they tell us plainly of what we have
already so often insisted upon,—namely, the redun-
dancy of this once continuous land with specific foci of
its own, and the sluggish or sedentary nature of those
primeval radiating forms.

We must not however omit to notice, that some few
of these endemic Helices appear to have been gifted (as
we should à priori anticipate) with more rapid capabi-
lities for diffusion than the rest. Thus, the H. erubescens \
and paupercula seem not only to have colonized the
entire province of which the Madeiras are detached frag-
ments, but to have even found their way to that distant
portion of it which now constitutes the Azores. The
H. polymorpha has also penetrated the Madeiran region
throughout; and being, like the H. erubescens, peculiarly
sensitive to the action of external influences, we per-
ceive, in consequence, that almost every island and rock
has now its own especial phasis of it. So greatly indeed
is that species beneath the control of local circum-
stances, that the very districts of an island as insignifi-
cant as Porto Santo have each their separate races to
boast of. On the Pico d’Anna Ferreira it assumes a |
form to which the name of H. attrita has been applied ;
when on the Ilheo de Baixo, it is the H. papilio; at the
Zimbra d’Areia, on the Pico de Conseilho, and in the
Ribeira da Coxinha, it is the H. pulvinata; and, in
many other situations widely removed inter se, it puts
on the shape (variable, both im size and hue) to which
the title of H. discina has been given. But, if we leave

134

Porto Santo, and follow this Protean Heliz into the
other divisions of the group; we meet with it on the
Dezertas as the H. senilis (those moreover from the
central island having a much more open umbilicus than
is the case in the northern and southern ones), whilst in
Madeira proper it constitutes the H. lincta (with an
additional pale variety for the calcareous district of
Canigal),—and. the H. saccharata, from the São Lou-
renço promontory.

In the same may we might pursue the H. erubescens,
and show that in the sylvan regions, and on the low
barren Ponta São Lourenço of Madeira, on the Pico
de Facho of Porto Santo, on the Ilheo Chão, on
the Central Dezerta, and on the Bugio (where it at-
tains a gigantic size), it has its distinct and permanent
phases,—the evident results of isolation, and other topo-
graphical influences, since the subsidence of the inter-
vening tracts. And in like manner, the Clausilia delto-
stoma is universal throughout the Madeiran Archipelago,
—displaying, however, in Porto Santo a fixed and
strongly ribbed, state, peculiar to that island. Thus, if
the examples which we previously cited tend to establish
the extreme slowness of the migratory movements of

the terrestrial mollusca across this former continent,
the present ones (which refer to a few exceptional
species of quicker self-diffusive powers) will show, no less
than the insects to which I have lately called attention,
that where sufficient areas had been overspread (before
the periods of subsidence) for the creatures to have

135

reached what now constitute the various islands of the
cluster, we at once detect traces of this fact, through
their more or less altered aspects, —the result of isola-
tion, and diminished range, during the enormous m-
terval which has elapsed since the successive convulsions
which caused the partial destruction of this Atlantic
province were brought to a close.

To return, however, to the insects, after this long con-

chological digression, —I need not multiply evidence, p le

corroboration of my theory. Enough has been said to
render intelligible the idea which I wished to convey,
concerning the general direction of the migratory current
over that ancient tract, and the extreme slowness of its
progress, —the former of which I consider probable
from the north-easterly course in which creatures generi-
cally identical were, if we may so express it, “ given-
off;” whilst the circumstance of their being for the
most part specifically dissimilar (or, in other words, of
the islands harbouring, many of them, species which
are endemic) would seem as it were to establish the
latter.

We must not however forget, that it is only to the
aborigines of this guondam land that the above specula-
tions apply. Assuming the region not to have been
insular, that is to say, to have been connected, on its
outer limits, with a European, or Mediterranean, conti-
nent; it would necessarily follow, that a certain number
of colonists must have found their way over its area,
and moreover in an opposite direction to the living

136

stream (if we may so call it) which had been long flow-
ing in a north-easterly course across its surface. What-

ever be the length of the periods, however, during which
these counter migrations were going on, I think it
sufficient to state that I would refer them to epochs
altogether different, —so that, accompanied as they may
have been by special geological phænomena, which, if
known, would in all probability become at once explana-
tory, we should be the less inclined to regard as absurd
what might appear at first sight difficult to understand.
In the case of the British Isles indeed, no less than five
of these distinct migratory eras have been assumed, and
specified *, by Professor Edward Forbes; therefore (what-
ever value be attached to his able and interesting theory)
I do not consider it necessary to apologize for requiring
at least two in behalf of this ancient Atlantic province.
Not to insist upon those of his faunas and floras which
are of a less evident, or more questionable, character,
he has at any rate proved, I think, almost to a demon-
stration, the westward progress of the great mass of our —
British animals and plants, over a then unbroken land
(the upheaved bed of the glacial sea), from the central
Germanic plains; whilst the accurate calculations of
the late Mr. Thompson of Belfast, concerning the reptile
statistics of Ireland, England, and Belgium, respectively,
have succeeded in showing, with much presumptive rea-
son, how the formation of St. George’s Channel, before

* Origin of the Fauna and Flora of the British Isles (in Mem. of
the Geol. Survey of Great Britain, vol. i. p. 336, A.D. 1846).

187

that of the German Ocean, interrupted the march of
these wanderers to the far West, and debarred an im-
mense proportion of them from an entry into Ireland,—
which would otherwise have colonized that country
equally with our own.

As regards Professor Forbes’s views of the creation of
a vast continent (reaching far into the Atlantic *) at the
close of the miocene epoch, through the upheaved bed
of a shallow miocene sea,—a region moreover of such an
extent as to have connected the various island groups
between the Fucus bank and the shores of the Old
World, not only with each other, but with a Mediterra-
nean province, Asturias, and even the south-west of
Ireland, —I must be content to pass them by, hazarding
only a few crude and desultory remarks. So large a

question, indeed, cannot be safely handled without
a corresponding amount of data, in all departments of

natural science, to reason from,—which I do not possess:
still, if a speculation from entomological premises, per
se, be not altogether worthless, I would point to the
conclusions (lately adverted to) which my Madeiran
researches have forced upon me, concerning the direc-
tion of the former insect migrations,—inferences which
are, from first to last, of necessity erroneous, if the
requisite medium for transit (into South-Huropean lati-

* « My own belief,” says Professor Forbes, “is, that the great
belt of gulf-weed, ranging between the 15th and 45th degrees of
north latitude, and constant in its place, marks the position of the
coast-line of that ancient land.”

ee ee a i

iraa

a i e E e

ye 138

tudes, at all events) be a mere conjecture or romance.
Such a notion, however, I would not for a moment
entertain,—for there is too much direct evidence in
support of distinct epochs of diffusion, to allow of any
hypothesis, when erideavouring to account for the
phenomena which we now behold, to supersede the
assumption of a once continuous tract. No matter if
we be compelled to suppose, whilst attempting to in-
terpret what we see, that the disseminating current has
flowed in exactly opposite courses, at different and
remote periods, over the surface of that ancient land,—
seeing that the fact (if such in reality it be) remains
untouched, that the land itself is at any rate there. I
am not, however, prepared to assert that the opinion at
which I had independently arrived, from the insect
statistics, does positively require a northerly prolonga-
tion of that area beyond the line of the central Mediter-
ranean districts; yet, after making every possible allow-
ance for accidental introductions since the subsidences
have taken place, there is still left a large residuum
which I am convinced can never be explained (unless
the doctrine of specific centres be a myth) except
through the means of ordinary and regular migration
over an unbroken continent. Nevertheless, though I
would not presume, from insufficient material, to insist
upon an extension of this Atlantic region into higher
latitudes than those which I have just referred to, I
must express my individual belief that, the more the
subject is examined, with reference to the distribution of

139

the Annulosa, the less will Professor Forbes’s idea suffer
from the inquiry. In the ‘Insecta Maderensia,’ I have
already thrown out a few scattered hints which bear on
this immediate consideration; and, since no subsequent
reason has induced me either to withdraw or modify
them (but rather the reverse), I will select the following,
—extracted from my preface to that work.

“Taking a cursory view of the Coleoptera here
described, the fauna may perhaps be pronounced as
having a greater affinity with that of Sicily than of any
other country which has been hitherto properly investi- |
gated. Apart from the large number of our genera i
(and even species) which are diffused over more or less ~“
of the entire Mediterranean basin, this is especially
evinced in some of the most characteristic forms,—such
as Apotomus, Xenostrongylus, Tarphius, Cholovocera,

Holoparamecus, Berginus, Litargus, Thorictus, and Boro-
morphus. There is, moreover, strange though it may
appear to be, some slight (though decided) collective
assimilation with what we observe in the south-western
extremity of our own country and of Ireland, —nearly
all the species which are common to Madeira and the

British Isles being found in those particular regions;

whilst one point of coincidence at any rate, and of a
very remarkable nature, has been fully discussed under
Mesites. Whether or not this partial parallelism may
be employed to further Professor E. Forbes’s theory of
the guondam approximation, by means of a continuous
land, of the Kerry and Gallician hills, and of a huge

140

miocene continent extending beyond the Azores, and
including all these Atlantic clusters within its embrace, |
I will not venture to suggest: nevertheless, it is impos-
sible to deny that, so far as the Madeiras betoken,
everything would go to favour this grand and compre-
hensive idea. Partaking in the main of a Mediterranean
fauna, the northern tendency of which is in the evident
direction of the south-western portions of England and
Treland, and with a profusion of endemic modifications
of its own (bearing witness to the engorgement of this
ancient tract with centres of radiation created expressly
for itself), whilst geology proclaims the fact that subsi-
dences on a- stupendous scale have taken place, by
which means the ocean’s groups were constituted; we
seem to trace out on every side records of the past, and
to catch the glimpses, as it were, of a veritable Atlantis
from beneath the waves of time *.”

* Although, for want of a better name, it may be admissible,
when speaking either figuratively or poetically, to allude to this
former region (as I have done in the above quotation) under the
title of “ Atlantis ;” yet it seems incredible that certain writers
(assuming its quondam existence) should have recently referred to
it seriously as the possible “ Atlantis of the ancients!” Consider-
ing that there is good reason to believe that all these islands were
islands in a miocene sea, and that, if (through a general elevation)
they were subsequently connected, the land of passage was broken
up long anterior to the appearance of man upon the earth, “ the
ancients”? must have assuredly merited their appellation, if they
could have thrown any light on a problem which belongs to an
epoch thus remote. Whether the “Atlantis” had any being at all
except in the imagination of the Latin poets, or whether (as Lord

141

The Mesites Maderensis, Woll., to which I alluded in
the above quotation, is undoubtedly a strong case in
point. Although specifically dissimilar from the M.
Tardii, its Irish counterpart, it nevertheless approaches
it so closely, that it might be literally mistaken, prima
facie, for that insect; and we know that it is one of the
plans on which Nature commonly proceeds, that species
which are not merely representative of (or analogous to)
each other, but which are actual homologues, or allies, |
should usually emanate at first from foci not far removed
inter se; or, at all events, if distant, connected by an

stantial item of the comprehensive scheme on which the
system of created things was originally planned. We

detect traces of this primary law in each division, or
class, of the organic world ; nor is its reality as a law
interfered with, through the occasional exceptions which
are liable, as in every other instance, to present them-
selves. Such deviations are often easily to be accounted.
for, whether by natural or artificial means; and do not

Bacon has suggested) it was the New World, will probably never
now be known; yet the fact that the Insule Fortunate of Juba are
almost universally identified with the present Canarian Group (as
indeed the accurate description of Pliny well nigh demonstrates),
and the Purpurarie with the Madeiras, ought at once, apart from
geological evidence, to point out the absurdity of the hypothesis,
that an Atlantic continent, in the very position which those islands
occupy, could have been acknowledged to have any existence by the
literature of either Rome or Greece. :

142

affect the subject, as a whole. Sometimes indeed they
become at once intelligible from the historical records |
connected with them, proving that human agencies have
been at work acting as transporting media, within a
period comparatively recent ; whilst at others, the fact
of the creature having been endowed with self-diffusive
powers to an extravagant degree may succeed equally in
rendering the phenomena explicable. But, even where
neither of these solutions would seem to suffice, we
should still recollect that it is only in the mass that such
questions can be pronounced upon; and that, con-
- sequently, where we are able to discover a rule which is
for the most part adhered to, it is more philosophical to
conclude that the departures from it are the result of
special disturbing causes (whatsoever they may have
been), than to permit them to undermine our faith in
what would be otherwise universally true. Thus, the
botanist tells us of Ixias, Stapelias, Mesembrianthe-
mums, Pelargoniums, and Euphorbias, as concentrated
in Southern Africa ; of Magnolias in Central America ;
of Calceolarias on the Andes; of Myrtles, Banksias,
Mimosas, and Eucalypti, in Australia; and of the
Bread-fruit Trees in the South Sea Islands: the orni-
thologist points, inter alia, to the Toucons and Hum-
ming-Birds from South America and the West Indies ;
whilst the student of the higher animals informs us of
the Kangaroos (indeed of the whole of the subclass
Marsupialia, except the genus Didelphys) as peculiar to
Australia and a few islands to the north of it; of Lemur

143

proper to Madagascar; of the Sloths, Armadillos, Tree
Porcupines, and of Alligators, and of the Platyrrhini
(amongst the Monkeys), to South America; and of the
Ourangs to the islands of the Indian Archipelago.

And so it is with the Insecta; many of the larger
groups of which (as Amycterus and Paropsis, in Australia;
Pachyrhynchus and Apocyrtus, in the Philippine Islands ;
Hipporhinus, Monochelus, Dichelus, and Moluris, in
Southern Africa; Macronota, in Java; and Naupactus,
Hypsonotus, Centrinus, Platyomus, and Cyrtonota, in
South America) are confined to countries of propor-
tionate magnitude, whilst the smaller ones are more com-
monly (asit were) shaped out for special provinces or re-
gions, according as local circumstances may require pri-
mary adaptations to harmonize with them. Thus, whilst we
frequentlyfind an extensive genus diffused over the greater
portion of the known world, we perceive that even its
structural characteristics are not uniform throughout, but
afford fixed geographical modifications (not, in this case,
however, the effect of development),—which have often,
in their turn, obtained the name of ‘ genera,’ and have
been described as such. Whether genera, however, or
not, they are undeniably small topographical assemblages,
satellites around their central types; and they may
therefore be safely regarded as genera, if we choose to
yiew them in that light. Of such a nature I have
already pointed out* is Saprinus, as compared. with
Hister ; Atlantis with Laparocerus; and Oxyomus with

* Insecta Maderensia, p. 214.

144

Aphodius; and, I might also add, Mesites with Cos-
sonus. I believe indeed that Mesites will be found to
attain its maximum on the Pyrenees (I already possess
two or three species, in abundance, from that region) ;
and, if such should be the case, we shall be able to ap-
preciate the significance of two representatives so closely
allied as the M. Tardii and Maderensis,—one of which
has been given off in the direction of Ireland, and the
other of the Madeiran Archipelago.

But I will not digress further on the subject of this
Atlantic province; since, however much I may indivi-
dually regard it as a reality of the past (which the
Coleopterous statistics have compelled me to do), it must
| of necessity remain, as heretofore, a matter of much
| controversy and doubt. I should indeed apologize for

“ | having trespassed on the reader’s attention, in wandering

! thus far from the immediate results of subsidences,—
which I proposed, at the outset of this chapter, to exa-
mine, with reference to the impeded diffusion of the
Annulose races. Nevertheless, concluding that a prac-
tical illustration of the effects of one of those great
downward movements to which geology so repeatedly
bears witness would not be irrelevant to the assumed
consequences which I had previously ventured to define,
I have acted on that judgment; and, having finished

my task, will now proceed to notice, briefly, a few other
considerations which should not be omitted, when
inquiring into insect distribution as influenced by geolo-

gical phenomena.

145

Next in importance, perhaps, to the elevations and
sinkings (traces of one or the other of which are more or
less manifest in almost every region of the world),
natural barriers may be cited,—as presenting, not un-
frequently, insurmountable obstacles to the self-dissem1-
nation of the insect tribes. By natural barriers, how-
ever, I would be understood to imply natural primary
barriers,—or, in other words, such as have continued as
barriers ever since the present animals and plants came
into existence upon the earth. For, the ocean (by way
of illustration) is a natural barrier ; and yet it is not
necessarily a primary one, as may be readily gathered
from the above remarks, in which the results of subsi-
dences are discussed,—subsidences which have had the
effect of letting it in over portions of an already tenanted,
and unbroken, continent. Mountain-chains, also, are
barriers; but it may happen that they have not been so
from the beginning,—as in instances, for example, where
they have been gradually upraised during periods geolo-
gically recent. But both sea and alpine ranges are
barriers, when (as usually happens) they have remained

as such since the creation of the several species which

now inhabit our globe. Mr. Darwin has acknowledged
this distinction, whilst commenting upon the marked
divergence of the faunas on the eastern and western
slopes of the Cordillera. “This fact,” says he, “ is In
perfect accordance with the geological history of the
Andes; for these mountains have existed as a great
barrier since the present races of animals have appeared ;
H

146

and therefore, unless we suppose the same species to
have been created in two different places, we ought not.
to expect any closer similarity between the organic
beings on the opposite sides of the Andes, than on the
opposite shores of the ocean. In both cases, we must
leave out of the question those kinds which have been
able to cross the barrier,—whether of solid rock or salt-

water

Conceding, therefore, this distinction between barriers

of a primeeval and more recent character, it is not diff-

cult to understand why the opposite sides of an alpine

chain, as well as countries separated by the sea, should

display different phenomena from each other. On the

contrary indeed, if we could feel satisfied that no means

of accidental transportation had operated to take them
there, and that the animals themselves were incapable of
enduring great diversities of temperature, and other con-

tingencies ; we should be startled to discover creatures
specifically identical in such regions,—so long at least as
the doctrine of unique centres of radiation formed part
of our zoological creed. We must not, however, be too
hasty in questioning (if I may be pardoned for the com-
pletion of a metaphor of which I thoroughly disapprove)

this article of our faith, through the occurrence of simi-

lar beings in areas between which there exist barriers,

both primary and well-defined; for the methods of
diffusion are so complicated and numerous, that, even
where human agency (that most important of elements)

* Journal of Researches, pp. 326, 327.

147

is not concerned, what at first sight may frequently
appear to be impossible becomes clear enough when
more critically inquired into. Some species, we know,
are gifted with greater powers for horizontal and vertical
progression than their comrades, and can (though they
are doubtless exceptions to the general rule) pass through
extremes of atmosphere sufficient to render even lofty
mountain summits no obstacles to them. Others, as the

Calosoma Syncophanta of Europe, have been stated to —

traverse the ocean unhurt* ; and I believe that many do
at times accidentally arrive, in a half-drowned state,
especially after boisterous weather, across channels of
considerable breadth. Mr. Kirby, on examining the
marine rejectamenta, during one of these apparent oc-
currences, along the Suffolk coast, writes as follows :
«Whether the insects I observed upon the beach, wetted

by the waves, had flown from our own shores, and, fall-
ing into the water, had been brought back by the tide ;
or whether they had succeeded in the attempt to pass
from the continent to us, by flying as far as they could,

* Many of the Calosomata would appear to possess this power
of crossing, either by flight or by abandoning themselves to the
waves (though more probably by the assistance of both), even ma-
rine barriers with impunity. Numerous instances are on record to
this effect ; and I am informed by Mr. Darwin that a Calosoma flew

on board the ‘ Beagle,’ off the Bay of San Blas, in South America, —
whilst they were ten miles from shore. It seems likely, therefore, |

that the occasional occurrence of the C. Syneephanta in our own
country, along the southern and eastern coasts, is due to this generic
capability,—and consequently (as indeed it is usually acknowledged
to be), the result of accident.

ay en te RES

148

and then fallmg had been brought by the waves, cannot
certainly be ascertained; but Kalm’s observation in-
clines me to the latter opmion*.’” And Sir Charles
Lyell remarks :—“ Exotic beetles are sometimes thrown
on our shdére, which revive after being drenched in salt
watert.” Nor should we forget that chance agencies of
every description, which we are too apt to overlook, are
daily at work (and have been so since, at any rate, the
last creative epoch) to transport these variously organized
beings beyond their original spheres. Sometimes they
are carried on, or within, the bodies of larger animals,
which is especially the case with the parasitic tribes; at
others on floatmg trunks of trees, and casual substances
of divers kinds, which are able to resist for a definite
period the destructive action of an element saturated
with salt. Unwilling victims, again, are ever and anon
hurried to comparatively distant lands by the very
winds that blow; and not only to distant lands, but
over altitudes in which the severity of the cold would
quickly annihilate them, were they (as perhaps usually
happens) to be deposited there on their headlong and
compulsory course. “ As almost all insects are winged,”
says Sir Charles Lyell, “ they can readily spread them-
selves wherever their progress is not opposed by un-

* Introduction to Entomology, ii. p. 13.

+ Principles of Geology, 9th ed. p. 657.

{ Although this is true on a broad scale, a reference to my ob-
servations in a preceding chapter will show, that in some countries,
especially islands, the reverse will frequently be found to obtain.

149

congenial climates, or by seas, mountains, and other

physical impediments ; and these barriers they can some-
times surmount by abandoning themselves to violent
gales, which may in a few hours carry them to very con-
siderable distances. On the Andes some sphinxes and
flies have been observed by Humboldt, at the height of
19,180 feet above the sea, and which appeared to him to
have been involuntarily carried into those regions by
ascending currents of air*.”” With respect to the acci-
dental conveyance of numerous species across the sea, it
is not to the winds alone that we must look for an ex-
planation. Large and rapid rivers are liable to inun-
date their banks and bring down insects in prodigious
masses,—which are disgorged into the ocean, and car-
ried to a distance from the coast, in proportion to the
violence of the ejecting stream. When the body of
water is considerable, the sea becomes diluted to an un-
usual extent; and creatures which must have otherwise
perished, from the action of the salt, are able to survive
for a time, and may be deposited, by means of rapid
currents into which they are borne, on neighbouring
islands and continents. Even the Hydradephaga are
thus occasionally transported; for Darwin mentions
having captured a Colymbetes off Cape S* Maria (to the
north of the Rio de la Plata), when forty-five miles
from the shore. And, in his ‘Journal of Researches,’
he records the following remarkable facts, which bear
upon this immediate question. “ On another occasion,

* Principles of Geology, p. 656.

150

when seventeen miles off Cape Corrientes, I had a net
overboard to catch pelagic animals. Upon drawing it
up, to my surprise I found a considerable number of
beetles in it, and, although in the open sea, they did not —
appear much injured by the salt water. I lost some of
the specimens; but those which I preserved belonged to
the genera Colymbetes, Hydroporus, Hydrobius, Nota-
phus, Cynucus, Adimonia, and Scarabeus. At first I
thought that these insects had been blown from the
shore; but upon reflecting that, out of the eight species,
four were aquatic (and two partly so) in their habits, it
appeared to me most probable that they were floated
into the sea by a small stream which drains a lake near
Cape Corrientes. On any supposition, it is an inter-
esting circumstance to find live insects swimming in the
open ocean seventeen miles from the nearest point of
land*.”

Accidental means of dissemination, such as those to
which I have just alluded, and others to which we might
appeal, will generally account, and with much presump-
tive truth, for the many exceptional cases which present
themselves, during our investigation into the effects of
natural barriers, as visible in the distribution of the

Annulose races, on the earth’s surface. I say “ excep-

tional cases,” because any one who has laboured practi-
cally in mountain tracts cannot have failed to recog-
nize the marked difference which is often displayed by
the imsect population on opposite sides of some alpine

* Journal of Researches, p. 159.

151

chain ; whilst he whose lot has been cast amidst island
groups, will have become even more conscious than the
former of the permanency of those impediments which
have been placed (in this instance by the broad arms of
the mighty ocean) as checks upon a too rapid system of
diffusion.

But if the sea and mountain ranges, when of a suffi-
cient age in situ, are amongst the most effectual of
Nature’s barriers against the self-dispersion of the
animate tribes; it follows that, if the two could be (as
it were) united, we should have found the greatest ob-
stacle which physical conditions can ordinarily present
against the wandering capabilities of the latter. The
question therefore arises,—Is it possible for them to be
so joined? Undoubtedly it is: and hence we arrive at
the conclusion, that a mountain island should afford us
the minimum of size, as regards the areas its species
have overspread, which any country is able to furnish.

Madeira is a mountain island,—its highest peaks
rising, although resting on so small a base, to an alti-

tude of more than 6000 feet. Yet it is only partially a

case in point; for, although it was a mountain mass,
and perhaps a very elevated one, when its endemic
beings made their first appearance upon its surface, we
have already intimated that it has become isolated since
that epoch: so that, whilst one of the natural barriers
against dispersion which it involves (namely, mountain
ridges) may be considered as primary ; the other (to wit,
the sea, as it now obtains) has played, as an agent of

152

obstruction, but a secondary part. Still, there is good
reason to believe that the ancient tract of which it is a
portion was broken up at a comparatively early date
after the creation of those peculiar organic forms which
found their birthplace within its bounds; and that, con-
sequently, the latter could not have wandered far (if we
except those species on which unusual powers of diffu-
sion were bestowed) when the land of passage began to
give way. Hence, even the sea, in this particular in-
stance, partakes almost of the character (no less than
the mountain heights) of an original impediment ; and
Madeira therefore may be safely quoted as an example
in which two barriers, of a primary nature, are united ;
and where, consequently, we may anticipate those ultra
phenomena of areal limitation upon which we have
been just commenting.

But let us now inquire, whether the hypothesis at
which we have arrived will stand the test of experience ;
for unless it will do so, we might have been spared the
labour of propounding it. Madeira is a country com-

posed of narrow mountain ridges, which radiate from
central crests, and form the lateral boundaries of deep

and precipitous ravines. Modifications of this structural
type are of course traceable everywhere; the upland
tracts are often undulating and broad, and the buttresses
which slope towards the sea are sometimes expansive
and irregular : yet upon the whole the above description
is correct, and we may accept it in a generic sense.
Now we may premise that, even to this day, it is an

153

island of floods; therefore, how much more must it
have been so when its primeval forests, in all their
splendour, caused an amount of exhalation and moisture
of which at present we can have but a remote conception !
Hence, it is hardly to be imagined, that (however limited
may have been the naturally acquired areas of those of
its inmates which are most sluggish and sedentary) a
fusion would not have taken place, in the course of ages,

so as to render its modern fauna, in a large measure,
homogeneous throughout. Yet, in spite of this esoteric |
tendency, it is surprising how little amalgamation has |
been effected amongst the tenants of its several districts. ||
\Scarcely a gorge or woodland serra exists within its i
bounds which does not harbour some species essentially ~
its own!! and in many instances the ranges of these

creatures are so local or confined, that they might
be easily overlooked even in their respective neighbour-
hoods. It is certain, however, that the floods (which
happen periodically) have done considerable work in
naturalizing many of the subalpine forms, which could
adapt themselves to the climatal change, in altitudes
below their normal ones: and, in the north of the
island, where the temperature is cooler than on the
opposite side, and where the lofty defiles terminate, even
at their lowest outlets, in abrupt precipices along the
coast, so that the rejectamenta during the annual rains
-are brought into direct contact with the shore, this
gradual process of deportation is particularly evident,—
a circumstance to which I have already alluded else-
HOD

154

where*, But, after making due allowance for these
powerful means of dissemination (which, in the common
order of things, must necessarily obtain in mountain
islands, as it were, par excellence), the fact still remains,
that in the Madeiran Group the acquired areas, even up
to the present date, of a vast proportion of the insect
inhabitants, are wonderfully circumscribed. The real
state of the case, however, would appear to be simply
this : that the floods, although they may have tended to
diffuse the members of a comparatively uniform alpine
fauna in the various clefts or gorges beneath, can have
had no power to combine the aborigines of the several
gorges themselves; and, since a large proportion of the
endemic species of those islands are (as I have previously
stated) apterous, the perpendicular edges of the ravines,
which in many instances rise to an elevation of 2000
feet, have acted (and ever will act) as impassable barriers
to vast numbers of the insect tribes.

With this single example (by way of illustration),
which the Madeiras have supplied, I will take my leave
of the question of natural barriers, as tending to regulate
the topographical diffusion of the Annulosa,—teeling that
I have already devoted too much time and space to this
portion of the subject (if such indeed it be) which I had
proposed in the present treatise to discuss. Other
barriers might have been adverted to,—such as large
rivers, extensive deserts, and thickly set forests (espe-
cially of pine-trees, which frequently offer a very decided

* Insecta Maderensia, p. 81.

impediment to insect progress) ,—but they are of
secondary importance, when compared with marine and
alpine ones; and their consequences may be, to a certain
extent, deduced from the considerations which I have
just entered into. My main object has been to draw |
attention to the fact, that the great obstacles which |
Nature has placed against the too rapid dispersion \
of animal life should be more strictly taken into account
(as a matter of positive reality) than it is, during our
investigations into entomological geography. To be
aware that these barriers exist, and yet to feel surprised,
especially in a country where the species are principally
wingless, that we do not discover indications of a general
uniformity in its fauna, involves an absurdity,—unless
the doctrine of specific centres of creation be a mere
coinage of the brain. But, if we believe in that theory
(which, until it can be shown to be impossible, I hold
that we are à priori bound to do), we must at least act
consistently with ourselves, and not anticipate pheeno-
mena where we have neither reason nor right to look
for them.

We are. too apt to draw a line of imaginary demarca-
tion between the sciences, as though each had its own
propositions to establish, and nothing more: indeed,

some of us would appear to assume (though perhaps —
tacitly), that what is proved to be true in one depart-
ment may be, at least, rendered inconsistent (if not
actually negatived) in another. But surely this requires
no argument to refute,—since a principle which is true,

156

is true under every circumstance and condition; for
otherwise, it could be both true and false. We need
not therefore be afraid of comparing truth with truth,
under whatever shape it may arrive, as though it were
possible that either of its phases could ever suffer from
the ordeal of a close contact; since, if they be really
true, and free from deception, they must needs go hand
in hand, and may become (however opposite they be in
their subjects) directly explanatory of each other. The
astronomer who is not intimately acquainted with pure
mathematical analysis, in its various aspects and
bearings, is in fact no astronomer at all. The geologist
who would interpret the grand phenomena of the earth’s
crust apart from statical and dynamical knowledge, and
without the help which the chemist, mineralogist,
anatomist, zoologist, and botanist can afford him, stands
a fair chance of leaving his problems unsolved ; whilst
the students of zoology and botany who would endeavour
to understand, and account for, what they see in the
animal and vegetable worlds around them, without
calling in geology to their aid, must assuredly be pre-
pared to fail signally in their attempts. All indeed
must work in concert, if the whole is to be advanced,—

and not only in concert, but as mutually assisting each
other. ‘By the help of truths already known, more
may be discovered; for those inferences which arise
from the application of general truths to the particular
things and cases contained under them, must be just.* ”

* ‘Religion of Nature Delineated, pp. 73, 74.

CHAPTER VI.

THE GENERIC THEORY.

How glorious to the observant eye is the great system
of the organic world, how perfect im each separate part,
how complete and harmonious the whole! The unity
of the comprehensive plan, amidst the infinite modifica-
tions which it includes, has ever been a theme of admi-
ration and delight ; for the mind, which has once caught
a glimpse, even in physics, of what it is not possible to

disprove, instinctively clings to it, as to a grand material
truth. The discovery, at all times, of what we feel to
be actually certain is in itself so fascinating, that the very
data which it gives us are scarcely more prized than the
mere knowledge that we have gained a single additional
light to guide us on our forward way: for, since in the
inductive sciences we can but climb from step to step,
at a slow and even pace, we hail with inward satisfaction
whatsoever may tend to lighten our task, and to lead us
more quickly onwards (gradually though we must of
necessity advance) towards its final accomplishment.
But how, it may be asked, is this general harmony of
the organic creation to be insisted upon, when beings so
extravagant and dissimilar are everywhere to be met

158
with? Is it possible to recognize anything like a unity
of type amongst creatures so differently constructed,
and so widely removed from each other in their habits,
aspects, functions, and attributes? Such questions as
these, however, though they may occasionally perplex
the tyro, or amateur, are not likely to be raised by any-
one who has mastered the merest alphabet of zoology,—
and who is aware that the integrity of Nature is some-
thing real and positive, as experience indeed is ever
tending more and more to corroborate, and by no means
the day-dream of an enthusiastic, or fertile, imagination.
To trace out the progressive development of animal life,
from its humblest phases; and to mark, as they become
visible in the intermediate grades, the first rudiments
of organs and instincts which are destined to attain
their maximum in the higher ones, embody but a small
portion of what it is the naturalist’s mission to investi-
gate. To him belongs the special privilege of inquiring
dogmatically into this structural advancement ; and of
suggesting methods of classification which shall accord,
in their several component divisions, so far at least as is
practicable, with the constitutional change. We should
recollect, however, that this system, being based upon
truth, must, if it would be consonant throughout, adapt
itself to all the various phenomena (in their respective
positions, in the scale), from the consideration of which
it should be exclusively deduced, or built. To draw
broad conclusions of any kind, or to attempt the esta-

blishment of propositions and principles, from simple

159

dialectics, without a previous training in the practical
bearings of the subject, would be absurd, and almost
certain to beget error. “It cannot be that axioms
established by means of reasoning [alone] should be of
any value for the discovery of new results; because the
subtilty of Nature far exceeds the subtilty of reasoning.
But axioms duly and orderly abstracted from parti-
culars, in their turn easily point out and mark off new
particulars; and so render the sciences active*.” Such
were the words of the greatest philosopher which this
country has ever produced ; and it would be well, whilst
examining the causes of what we see, and endeavouring
to obtain some faint and distant notion of the vast
scheme of Nature as originally designed, to keep them
constantly in view,—lest, by trusting to theory only,
apart from observation and facts; or by venturing to
pervert the latter (instead of being led by them), so as
to tally with our preconceived ideas of what ought to be,
we miss our road, and become lost in the mazy labyrinth
of our own fanciful inventions.

With this preliminary stricture on the express duty
which devolves upon the naturalist (with whom the

phenomena of the organic world principally rest, for
interpretation) to make facts, rather than reason and

* «Nullo modo fieri potest, ut axiomata per argumentationem
constituta ad inventionem novorum operum valeant; quia subtilitas
naturæ subtilitatem argumentandi multis partibus superat. Sed
axiomata a particularibus rite et ordine abstracta, nova particularia
rursus facile indicant et designant; itaque scientias reddunt ac-
tivas.” — Novum Organum, Aphoris. xxiv.

160

argument, ‘the basis of his various doctrines,—at any

rate of those in which the critical subject of arrangement

is concerned; I shall perhaps be pardoned, after having
been drawn, in the preceding chapters (however involun-
tarily), into the question of ‘species,’ as rigidly defined,
if I now offer a few passing remarks on the theory of
genera.

There can be no doubt that amongst a large class of
ordinary observers a clear perception of the generic
system, in an abstract sense, does not by any means
prevail, What the nature of a genus really is, would
appear to have been very commonly overlooked, or per-
haps misunderstood, by people of this stamp; and the
consequence has been, that the wildest notions have
frequently arisen, even from men of sound specific
attainments, as to the claims (for annihilation or re-
tention, as ‘genera’) of certain subsidiary zoological
assemblages. The terms ‘genus’ and ‘species’ have
been conjointly so long associated in our minds with the
selfsame things (whatsoever they may be), that they
have become almost part and parcel of the objects them-
selves; so that the student who. does not sufficiently
reflect on their true signification, is apt to regard them
as of equal importance,—or, rather, more often perhaps
than otherwise, to make the latter subservient (or
inferior) to the former! This however is, in reality, the
very reverse of what should be the case, as a moment’s
consideration will indeed at once convince us: for what
are genera, after all, but dilatations (as it were) along a

161

chain which is itself composed of separate, though dif-
ferently shaped, links? The links (or the actual, inde-
pendent bodies which constitute the chain) are the
species ; but the knobs, or swellings, which their several
forms may tend, by degrees, to establish along its course
(through the slight disparity which each of them pre-
sents from that which is next in succession to it; and
therefore through the gradual manner in which the
bulbs, or nodules, may be said, on the whole, to be pro-
duced), are the groups into which those species naturally
fall. It matters not a straw whether these assemblages
be primary, secondary, tertiary, &c.,—in other words,
whether they be departments, families, or genera, as
usually understood,—the principle is in every instance
the same; the difference bemg merely relative, and not
absolute.

Or, if we choose to vary the simile, we may compare
the whole system to a cord, upon which beads, of innu-
merable sizes, patterns, and colours, have been densely
strung. Now, if there were no such things as natural
divisions in the organic world, these beads (which repre-
sent the separate species) might have been disposed of
anyhow,—their positions, with respect to each other,
would under those circumstances have been of no im-
portance, But such is not the case: there is an order
and method throughout Nature, which shows that every
individual portion of it has been adjusted by the Master’s
hand, and that nothing has been left to chance. Those
beads (to follow up the metaphor) of countless magni-

162

tudes and hues, have had their proper places allotted to
them,—and moreover with such care and regularity, that
a complete plan, or scheme, of distribution is at once
conspicuous. Although there are not even two, amongst
that enormous multitude, which are precisely alike (for
every species, however it may resemble its next ally, has
some distinctive feature of its own), we immediately per-
ceive that those beads which have most in common, are,
as it were, attracted to each other,—so as, by their close
approximation, or contact, to create excrescences and
stripes, of divers kinds, along the entire length of the
cord. If we assume now that the red beads have been.
collected together, to the length (for instance) of a yard,
and that within that space a dozen protuberances, of
discordant aspects and dimensions, have (by the union
of those beads which more nearly simulate each other)
been brought about; we shall have a very fair idea of
the ordinary grouping of the animate tribes. The red
beads, taken in the mass, may be likened to a perfect
“family ;” the differing gibbosities to twelve well-marked
“genera,” which that family includes; whilst the
“species” (the real dramatis persone, of independent

existence, which are nevertheless compelled to occupy
the situations we have described,—thus causing the divi-
sions to be mapped out) are here typified, as everywhere,
by the several beads themselves.

I have not thought it necessary to pursue this reason-
ing into higher divisions than “ families ;” but of course
it may be extended to any amount,—so as to shadow

163

forth, equally, the compartments of primary significance.
Nor would I wish to imply, by the above similes, that I
regard a lineal method of arrangement as the correct one.
Every zoologist is aware, that in Nature such does not
exist: but the mode of illustration which I have selected
is applicable to all systems alike, so far as the principle
is concerned.

It will consequently be seen, from what has been said,
that the terms “genus” and “ species » not only differ
very considerably in importance, but in signification also.
Whilst the former is merely suggestive of a particular
position which a creature occupies in a systematic scale
(a position, however, which depends upon the various
structural peculiarities which it possesses i2 common with
other beings,—which thus more or less resemble it); the
latter expresses the actual creature itself: so that while
one applies to several animals (of distinct natures and
origins, though bound together by a certain bond of
imitation), the other belongs to a single race alone, which
it therefore exclusively indicates. But if such be the
case, it will perhaps be asked,—Why then insist upon a
generic name at all, if the specific one be sufficient to
denote all that is required, namely, the animal itself? To
which, however, we may reply, that the binomial nomen-

clature is demanded for two elementary reasons,—first,
because it is founded upon a natural truth, which (to say
the least) it would be unwise to violate ; and, secondly,
because it is convenient, both for simplification and

analysis. We should assuredly be surprised were a man

164:

to object to his surname, as unnecessary, because he has

a christian (or specific*) one which is the exponent of ©
him alone. True it is that his family (or generic) title
applies to the rest of his kin also; but, since there are
other people (of other families) who may have the same
individual appellation as himself, it is clearly desirable,
even as a matter of expediency alone, that patronymic
and christian name should be alike retained. We need
not, however, plead expediency, in favour of this accept-
ance of what has been so long tested, and shown to be
correct ; we appeal to a higher tribunal,—that of expe-
rience,—in proof that it draws its origin from Nature
itself, and is implied by the very existence, or reality, of
natural groups. The ‘Méthode Mononomique’ has indeed
been attempted+; and it has failed,—or at any rate it
has shown itself to be inferior, both ideally and in prac-
tice, to the plan commonly in use: and if I might be
pardoned a passing conjecture on its ultimate success, I
should be inclined, since it is contrary to the canon of
the organic world, to regard its case as utterly hopeless.

Let us not be unfair, however, towards those who have
sought to establish a nomenclature which they conceived
would be less open to objections than that which we have
been hitherto accustomed to endorse. The notion did,

* In selecting this simple method to illustrate the principle of a
binomial system of nomenclature, it is scarcely necessary to remind
the reader that I do not intend to imply that every man is specifically
distinct from his neighbour !

+ Considérations sur un Nouveau Système de Nomenclature, par

C. J. B. Amyot (Rev. Zool., p. 133, A.D. 1838).

165

at any rate, arise out of an apparent defect m the bino-

mial process,—for the inconveniences which they com-
plained of are real ones ; and, having felt them practi-
cally, they aspired to sweep them away by remodelling
the whole system afresh. But, had it not been for an
evident misconception of the generic theory, in the
abstract, the trial would in all probability have never
been made; and we should have been spared the downfall
of a contrivance which has had but little to recommend
it beyond the ingenuity of its machinery and detail. If
we analyse the motives for this experiment, we shall find
that it originated from a belief, that genera are either
purely imaginary, or else that they must (like species)
have a definite and isolated existence. Now both of
these conclusions appear to be equally gratuitous and
untenable; and such as a lack of observation could alone
beget. Genera are not mere phantoms of the brain (as
most naturalists will readily admit) ; but they are, like-
wise, by no means abrupt, or well-marked, on their
outer limits (except indeed by accident,—of which here-
after), but merge into each other by gradations, more
or less slow and perceptible. Such being the case, we
can easily understand why it is that the followers of the
‘Méthode Mononomique’ (who, paralysed by the fact that
genera are seldom clearly defined at their extremes, would
seem to repudiate them in toto) have rashly regarded. the
binomial system as intolerable. Finding that it was
possible for numerous species, whose structural charac-
teristics were less conspicuously pronounced than those

166

of their allies, to be enumerated, and with equal plausi-
bility, under two consecutive groups; they immediately
inferred that the groups themselves could not be upheld
on account of these connective links: and so it was re-
solved (through a new and artificial scheme) to ignore
them; and to fall back upon the creed, that species alone
(and not genera) are to be recognized in the organic
world. This was but the device, however, at the outset,
of a single mind; and the perverts to it have been but
few. It is in direct opposition to the first principles of
nomenclature, and sets at defiance a great natural truth.

But what, it may be inquired, is this great primary
truth which the monomial system tends to violate? I
repeat what I have already stated, that it is the existence
of natural assemblages which that scheme would, if it
were practicable, discountenance. Order and symmetry,
however (which involve classification, or arrangement),
are the law of Nature, and it is not possible to set them
aside. It matters not if harsh lines of demarcation are
undiscernible between the several consecutive groups,—
the groups themselves must still remain (however equivo-
cal it may be where they exactly commence or termi-
nate), and cannot be wiped out. To suppose à priori

that the allied divisions of the animate creation are per-
fectly disconnected infer se, is in fact to break the chain
on which the unity of the organic world depends; whilst
to assume that groups cease to be groups when they can
be discovered to merge into each other, would no less
destroy the harmony of that admirable method, or

167

array, which the naturalist, above all others, delights to
contemplate. If things are no longer to be regarded as

dissimilar because they unite on their outer limits,

differences may be given up, as having no special
meaning, and as therefore unworthy of investigation.
It requires but a slight insight into the physical universe
to be convinced, that nearly everything which we see
(and, moreover, without injuring its individual reality) is
blended into that to which it is the most akin. Night
is distinct from day; yet, so long as the twilight inter-
venes, no man can pronounce where the one ends, and
the other begins. Heat is opposed to cold; yet, if by
degrees they be respectively diminished, they will at last
amalgamate, in a central temperature. And thus it is
with things material. The sea and the land are essen-
tially unlike ; yet the precise boundary between the two
is never clearly defined,—the ebb and flow are constantly
going on, and the line of separation is variable. The
mountain-range is moulded on a different type to the
level country beneath it; yet the turning-point of them
both is, in all instances, on neutral ground. We need
not however adduce further evidence in support of this
fact,—that, throughout the whole of Nature, the general
principle of fusion (either absolute or apparent) 1s most
obyious. From first to last, traces of it are everywhere
to be detected; not only between clusters, OY material
combinations, of objects (in which case it is absolute),
but even between the objects themselves,—under which
circumstances, however, it is merely apparent; for, since

168

they are specifically dissimilar, it can only arise from

their near resemblance to each other, and not from their
positive coalescence. But, admitting that this universal
blending, throughout the animate world, does not inter-
fere with the gradual conformation of its several groups,
which therefore should be recognized; we may perhaps
be told by the believers in the ‘ Méthode Mononomique,’
that they do not intend to ignore the arrangement which
Nature has so broadly laid down, but that, on the
contrary, they tacitly endorse it,—their device having
reference to the names only. To this however it will be
sufficient to reply, that, if they deem it necessary (of
which I am by no means convinced) to accept the
natural genera of the organic creation at all, why not
acknowledge them? and how can they be so well
acknowledged, either in principle or practice, as through
the medium of a binomial nomenclature? Such a
system is the only consistent one, on the hypothesis that
they do consider them of primary importance ; it is
more in unison with our notions of what ought to be ;
more suggestive of what actually is; more honest and
generous to those who have laboured (as describers), with
such care and diligence, before us.

It will be perceived, from the above remarks, that,
altiðugh professedly criticizing the ‘Méthode Mono-
nomique,’ into the analysis of which my subject has
unintentionally drawn me, it is the absurdity of ob-
jecting to genera because they are not rigidly defined
throughout, that I have been mainly striving to con-

169

demn. It is indeed well nigh incredible that any such
strictures could ever have been advanced; for it must
surely have occurred to the most superficial inquirer,
that genera, after all, cannot be homogeneous,—seeing

that they are necessarily composed of detached species,

no two of which are precisely similar, even in the few
structural details which may have been accidentally
chosen for generic diagnostics. How is it possible,
therefore, that mere groups, even though they be in
accordance with Nature, should be so far isolated and
uniform in their character as to occupy an analogous
position to that of the absolutely independent species (of
distinct origins) which they severally contain ?

Taking the preceding considerations into account, the
question will perhaps arise,—How then is a genus to be
defined? To which I may reply that, were I asked
whether genera had any real existence in the animate
world, my answer would be that they undoubtedly have,
—though not m the sense (which is so commonly
supposed) of abrupt and disconnected groups. I con-
ceive them to be gradually formed nuclei, through the
gathering together of creatures which more or less
resemble each other, around a central type: they are
the dilatations (to use our late simile) along a chain
which is itself composed of separate, though differently
shaped links,—the links being the actual species them-
selves, and the swellings, or nodes, the slowly developed

genera into which they naturally fall. When I say
I

170

“slowly developed,” my meaning may possibly require
some slight comment. It is simply therefore to guard
against the fallacy, which I have so often disclaimed,
that genera are abruptly (or suddenly) terminated on
their outer limits, that the expression has been employed.
Though I believe that a series of species, each partially
imitating the next in contact with it, is Nature’s truest
system; yet we must be all of us aware that those
species do certainly tend, in the main, to map out
assemblages of divers phases and magnitudes, distin-
guished by peculiar characteristics which the several
members of each squadron have more or less in common.
So that it is only in the middle points that these various
groups, respectively, attain their maximum,—every one
of which (by way of illustration) may be described as a
concentric bulb, which becomes denser, as it were, in its
successive component layers, and more typical, as it
approaches its core.

If, then, the theory of genera be such as I have endea-
_voured to expound, it results from what has been said,
that every generic type is to be looked for in, or about,
the centre of its peculiar group,—or at any rate in that
region of it which would seem to be the most charac-
teristically, or evenly, pronounced. I lay particular
stress upon this conclusion, because (if correct) it will
somewhat modify the notions which are occasionally
entertained upon the subject. A stricture, however,
may here be required upon what I have advanced, lest,

through using the metaphors which I selected for the
elucidation of a principle, it be supposed that I would
wish them to apply to the smaller details, likewise, of
the problem. If a genus has been portrayed under the
similitude of a bulb, or of a nodule (formed by the ap-
proximation of beads which more or less resemble each
other in their primary aspect), it does not follow that
either bulb or nodule are to diminish in a similar ratio
towards their respective circumferences,—or, which is the
same thing, that they are to be symmetrical ; whether
spherical, ovoid, or otherwise. The general method of
the organic creation is a progressive one; and its suc-
cessive types, therefore, will not always be found to
radiate equally from their normal foci: so that it is in the
direction of the higher (rather than the lower) extre-
mities of the assemblages that those foci are usually to
be discerned ;—and where the groups are large, it is not
often difficult to pronounce which of their ends are, as a
whole, the more perfectly developed.

It will, moreover, be further acknowledged (if my
premises are allowed), that, since it is a somewhat
central position|which the typical member of a genus
usually occupies, the diagnostic characters, although (in
combination) carried out to the full, are more evenly
balanced in a generic type than in any of its associates ;
or, in other words, that a species in which any single
organ is monstrously enlarged, at the expense of the
rest, is seldom typical of the assemblage with which it is

placed ; but may be à priori regarded as in all proba-
? i

lid

172

bility a transition form, leading us onwards into some
neighbouring group*.

I will not, however, venture too closely into this ques-
tion in its minor bearings ;—suffice it to have demon-
strated that, whatever be the rate, law, or direction, of
the advancement of the various groups towards a more
perfect model ; or in whatsoever position the several types
are to be discerned, with respect to their immediate
associates, genera cannot be isolated and distinct, but
must of necessity merge (each into two or more others)
on their outer limits. Hence, if such be the case, as I
contend that it usually is (the exceptions to the rule
being, as I shall hope shortly to prove, the result of

it may perhaps be a problem, how far we are justified in
rejecting many large and natural assemblages, through
the fact that they blend, both at their commencement
and termination, imperceptibly, with others,—their pre-
cise boundaries being dimly defined.

That the recognition of genera is necessary, even as

a matter of mere convenience, is self-evident; for in
many extensive departments they combine with each other
so completely at their extremities (although sufficiently
well-marked in the mass), that, unless we are prepared

* T may add, that this suggestion, as to the evenly balanced state
of generic types, is in accordance with the views of Mr. Waterhouse,
—whose extensive knowledge in the higher departments of zoolo-
gical science gives a value to his opinion, especially on questions
such as these, which I am glad to have an opportunity of acknow-
ledging.

173

to accept them as they are, we must needs repudiate
them altogether: under which circumstances, our diffi-
culties, both in determination and nomenclature, would
be increased tenfold. We should also recollect, that
clusters which seem abruptly chalked out whilst our
knowledge is imperfect, are very frequently united with
others when fresh discoveries are made, and the inter-
mediate grades brought to light: so that their apparent
isolation may oftentimes arise from our iguorance of the
absent links, rather than from the fact itself. It would
surely be more desirable, therefore, when viewed even
in the light of expediency alone, to submit to the possi-
bility of a few neutral species being conceded, with equal
reason, to different groups, than to amalgamate the
whole, and so lose sight of the general method or

arrangement, into which the various creatures do un-
questionably (in a broad sense) dispose themselves. If,
however, there be any truth in the generic doctrine
as above enunciated, the question of convenience may be
omitted from our speculations in toto,—seemg that all \

genera (except those whose present abruptness is the
effect of accident) fuse into others with which they are
in immediate contact: so that in reality, unless we
ignore these natural assemblages from first to last, we
have no choice left us as regards the equivocal forms ;
but must consent to recognize them as of doubtful loca-
tion, and as possessing an equal right to be placed im
one or the other of two consecutive groups,—according

174

to the judgment of the particular naturalist who has to
deal with them.

But let us glance at the subject through the medium
of an example, and endeavour to realize what would be
the consequence of that wholesale combination at which
we must sooner or latter arrive, if genera are not to be
upheld because they slowly merge into each other as we
recede from their respective types. The immense de-

partment Carabide, of the Coleoptera, is eminently a
case in point. In the details of their oral organs the
whole of that family display (as I have elsewhere* re-
marked) so great a similarity inter se, or rather shade
) off into each other by such imperceptible gradations,
) that the tendency which various clusters of them possess
to assume modifications of form which attain their max-
imum only in successive centres of radiation, must often-
times be regarded as generic, if we would not shut our
eyes altogether to the natural collective masses into
which the numerous species (however gradually) are, in
the main, so manifestly distributed. It is possible
indeed that, as our knowledge advances and new dis-
coveries take place, we shall so far unite many of the
consecutive nuclei which are now considered pretty
clearly defined, that we shall be driven at last either to
accept the Linnzean genera only, or else the entire host
of subsidiary ones (albeit perhaps in a secondary sense)
which are, one by one, being expunged. And, since
* Annals of Nat. Hist. (2nd series), xiv., p. 199.

175

under the former contingency the determination @ f species
would become practically well nigh hopeless, it is far
from unlikely that we shall eventually hail the latter as,
after all (at any rate to a certain extent), the more con-
venient of the two. Look, for instance, at the great

genus Pterostichus, which has nearly 200 representatives :

in Europe alone: true it is that its several sections

(Pecilus, Argutcr, Omaseus, Corax, Steropus, Platysma,
Cophosus, Pterostichus proper, Abax, Percus, and Molops),
although easily recognized in the mass, do unquestionably
blend into each other; yet I believe that it has arisen

from a too rigid promulgation of the generic theory /

that they have not been retained as separate. And this
opinion may be rendered somewhat more plausible,
from the knowledge that certain of the Pterostichi (the
Argutors, for instance) approach so closely, im their
trophi, to Calathus, as to be hardly discernible from it ;
which latter genus is scarcely distinguishable (struc-
turally) from Pristonychus,—a form which, in its turn,
leads us on towards another type. Who would have
imagined, again, some fifty years ago, that the widely
distributed groups, Calosoma and Carabus, were not
thoroughly detached inter se? yet what naturalist now
can draw an exact line of demarcation between them ?
And so it is with numerous others, which it is needless
to recall. The practical inference, however, from the
whole, is this: that if genera must be rejected because
they are not homogeneous and isolated throughout, the

176

only ones that will remain are those which have become
abrupt from causes which are merely accidental.

Having now, however, examined the question in its
broadest phasis, that is to say, on the supposition that
Nature is complete in her several links and parts; I
shall perhaps be expected to offer a few passing words
on what I have already hinted at,—namely, the possi-
bility of genera being absolutely well-defined, even on
their outer limits, from accident. Briefly, then, it is
through the extinction of species that groups may, in
some instances, be abruptly expressed: but, as such
contingences are at all times liable (whether from
natural or artificial causes) to happen; it would be
unfair to build up our generic definition from examples
which are the exception, and not the rule,—and, more
than mere “ exceptions” (as commonly understood by
that term), the result of positive disturbances from
without. Yet, that genera thus distinctly bounded, at
either end, do actually occur, must be self-evident to
any one who has attempted to study the distribution of

organic beings with reference to the geological changes
which have taken place on the earth’s surface ; for it is

clear that a vast proportion of the creatures which
inhabit our globe came into existence at periods anterior
to many of those great convulsions which altered finally
the positions of sea and land, apportioning to each the
areas which they now embrace: so that, if generic
provinces of radiation (no less than specific centres) be

ay a.

more than a fancy or romance, it is certain that nume-
rous members of many geographical assemblages must
have perished for ever during the gigantic sinkings
which have at various epochs been brought about. From
which it follows, that those groups, or clusters, of which
but few representatives (comparatively) are extant, will
be more or. less abruptly terminated, according as the
original type to which they severally belong was peculiar,
and in proportion as the number of its exponents has been
reduced.

Although there are many means through which
species may become annihilated, yet, since the sub-
sidence of a tract into the sea involves the maximum of
loss which a space of that magnitude can sustain, the
above conclusion gives rise to a corollary: that tt is in
islands that we should mainly look for genera which
are to be rigidly pronounced. The question therefore
naturally suggests itself,—Is this in harmony with what
we see; or, in other words, is it consistent with ex-
perience, or not? I believe that it is; for I think it
| will be found, on inquiry, that the greater proportion of
| those groups which are more especially isolated in their
| character (I do not say, necessarily, the most anomalous ;
| though this in some measure follows from the fact of
their detachment) are peculiar to countries which are
insular.

But, however important an element, in the eradica-

tion of species, submergence may be; we must not
entirely omit to notice other methods also, through the
19

178

medium of which genera may become well-defined. We
should recollect that the removal of a very few links
from an endemic cluster is sufficient to cause its dis-
junction from the type to which it is next akin, and that
where the creatures which unite in composing it are of
slow diffusive powers, or sedentary habits, the elimina-
tion of such links is (through the smallness of the areas
which have been overspread) a comparatively easy opera-
tion. The accidental introduction of organic beings
amongst others to the interests of which they are hostile,
may be a powerful means, as Mr. Darwin has suggested,

of keeping the latter in check, and of finally destroying
them*. The gradual upheaval of a tract which has
been well-stored with specific centres of radiation,
created expressly for itself, may (through the climatal
changes which have been brought about) succeed in
extirpating races innumerable,—those only surviving
which are able to adapt themselves to the altered condi-
tions ; and which would now be consequently looked
upon as abrupt topographical assemblages. The over-

* A familiar example of this disappearance of a creature before
the aggressive powers of another, which is either hostile to or stronger
than itself, is presented by the Black Rat (Mus rattus) of our own
country,—which is said to have been extremely abundant formerly,
but which is now replaced by the common brown (or “ Hano-
verian”) one of Northern Europe. The British species, however,
although it has become extremely scarce, is not yet quite extermi-
nated: it has been recorded (vide ‘ Zoologist, 611) in Essex, and in
Devonshire (‘ Zoologist, 2344); and it still swarms on a small rock
off Lundy Island, in the Bristol Channel. It is reported, moreover,

' to have been lately re-introduced at Liverpool.

179

whelming effect of a volcanic eruption, in a region
where the aborigines of the soil have not wandered far
from their primeval haunts, may, as Sir Charles Lyell
has well remarked, put an end to others, and so effect
the separation of their allies from the central stock.
And, lastly, the intervention of man, with all the various
concomitants which civilization, art, and agriculture
bring in his train, is the most irresistible of every
agency in the extensive (though often accidental) demo-
lition of a greater or less proportion of the animate
tribes.

The whole of these ultimate assortments, however, are
dependent, as it were, for their outline, upon contingency
or chance; and we must not deduce our ideas of genera
from the examples which they supply. We should
rather reflect, that it is no matter of mere speculation,
that many organic links, now absent, have, through the
crises and occurrences to which we have just drawn
attention, become lost. On the contrary, indeed, we
know that, in the common course of things, 1t must
have been so; and therefore we are induced to regard
those cases as exceptional, and as in no way expository
of Nature’s universal scheme. The more we look into
the question, whether by the light of analogy or the
evidence of facts, the more are we convinced that lines
of rigid demarcation (either between genera or species,
though éspecially the former) do not anywhere, except
through accident, exist. And hence it is that we ascend,
by degrees, to a comprehension of that unity at which I

180

have already glanced; and are led to believe that, could
the entire living panorama, in all its magnificence and
breadth, be spread out before our eyes, with its long-lost
links (of the past and present epochs) replaced, it would
be found, from first to last, to be complete and continuous

throughout,—a very marvel of perfection, the work of a
Master’s hand.

CHAPTER VII.

Deposita sarcina, levior volabo ad colum.—S. Jerome.

Havine now completed the short task which I had
undertaken to perform, I will, in conclusion, offer a few
brief comments on the results at which we have arrived,
and endeavour to realize to what extent the considera-
tion of them is likely to be found useful, durmg our
inquiries into the general subject of entomological
geography.

Commencing with the thesis, that specific variation,
whether as a matter of experience or as probable from
analogy, does ipso facto exist; I have endeavoured to
maintain that position, by evidence of divers kinds; and
I have sought to strengthen the inferences deduced, by
an appeal to some of those external agents and circum-
stances which may be reasonably presumed (if not
indeed actually demonstrated) to have had a consider-
able share in bringing it about. I have also suggested
what the principal organs and characters are, in the
Insecta, which would appear to be more peculiarly
sensitive to the action of local influences ; and I have
then diverged to the question of topographical distribu-
tion, in connection with the geological changes on
the earth’s surface; and, lastly, to some practical hints

182

arising out of a proper interpretation of the generic
theory. How far I have succeeded in elucidating the
several points which I proposed to examine, is a problem
which must be solved by others; meanwhile, if I have
failed at times to interpret what seems scarcely to admit
of positive proof, I shall at least have had the advantage
of propounding the enigmas for discussion, and of so
paving the way for future research. We must remember,
however, that, where certainty is not to be had, proba-
bility must be accepted in its stead ; or, as an old writer
has well expressed it: “That we ought to follow pro-
bability when certainty leaves us, is plain,—because it
then becomes the only light and guide that we have.
For, unless it is better to wander and fluctuate in abso-
lute uncertainty than to follow such a guide; unless it
be reasonable to put out our candle because we have not
the light of the sun, it must be reasonable to direct our
steps by probability, when we have nothing clearer to
walk by *”’,

What my chief aim in the present treatise has been,
will be easily perceived,—namely, to substantiate, as
such, those elements of disturbance (on the outward con-
tour of the Annulose tribes) with which the physical
world does everywhere abound: and, thereupon, to pro-
voke the inquiry, whether entomologists, as a mass, have
usually taken them into sufficient account, when de-
scribing as “species,” from distant quarters of the
globe, insects which recede in only minute particulars

* Religion of Nature Delineated, p. 103.

183

from their ordinary states. My own impression is, that
they have not done so; and, moreover, that, if they
had, our catalogues would have worn a very different
appearance to what they now do: for, when once the
subject is fairly looked into and analysed, it is impossible
not to be convinced, that the primá-facie aspect of these
creatures is eminently beneath the control of the several
conditions to which they have been long exposed. But
let me not be misunderstood in the conclusion which I
have been thus compelled to endorse, or be supposed to
ignore the fact that truly representative species may
frequently occur in countries far removed from each
other; which cannot therefore be regarded as modifica-
tions of a common type. I believe, however, that this
doctrine of representation, whatever truth it may con-

tain, has been too much relied upon; and that we have
been over-ready to take advantage of it (unproved as it
is) for the multiplication of our, so called, “ specific
novelties.” I suspect, indeed, that actual representative

species (if they may be thus expressed) are more often
to be recognized on the isolated portions of a formerly
continuous tract, than in regions which have been widely
separated since the last creative epoch ; and that, in the
instances where beings of a nearly identical aspect are
detected in opposite divisions of the earth, it is more
often the case that members of them have been trans-
ported at a remote period (either by natural or artificial
means) from their primeval haunts, and have become
gradually altered by the circumstances amongst which

Ses cae we ~~ y s aa a ve
SS a eee ———

184:

they have been placed, than that the respective phases
were produced in situ on patterns almost coincident.

I have before announced my conviction, that generic
areas have a real existence in Nature’s scheme; and
that, consequently, where species which are so intimately
allied that they can with difficulty be distinguished,
prevail, there is presumptive reason to suspect (until at
least the contrary is rendered probable) that the areas
which they now colonize were once connected by an
intervening land,—or, in other words, that the migra-
tions of the latter were brought about, through ordinary
diffusive powers, from specific centres within a moderate
distance of each other. I say “presumptive. reason,”
because there are undoubted exceptions to this law (as
to every other), and it can therefore be only judged of
on a broad scale. Still, I contend that in a wide sense
it holds good ; and that, consequently, if closely related
“ species” are traceable in countries which geology
demonstrates to have been far asunder during the entire

interval since the first appearance of the present animals

and plants upon our earth, there is at any rate an
à priori probability that they are no species at all,—but
permanent geographical states, which have been slowly
matured since their casual introduction beyond their
legitimate bounds. :

If we except those forms which are in reality but
modifications, from climatal and other causes (and
which have, therefore, been wrongly quoted as distinct) ;
I believe that a vast proportion of the species which

185

have been usually considered to be “ representative ”
ones, were members, in the first instance, of the self-
same assemblages,—which had wandered to a distance
from their primeval haunts, and were afterwards,
through the submergence of the intervening land, cut
off from their allies. I have adduced, in a preceding
chapter, some remarkable examples in illustration of
this hypothesis,—an hypothesis which I believe to be
the true clue to a very large item of the “ specific

representation” theory. A considerable number of the ~ Lar

Madeiran Helices may be cited (which I have already
done*) as, in the strictest sense, representative of each
other,—and as therefore specifically distinct : and I
may add, that it is to island groups that we must
mainly look for this system in its full development.

But, apart from the fact that I would not wish to
resign in toto the doctrine of “ specific representation,”
even as frequently understood (that is to say, as recog-
nizable in countries which have been altogether dis-
connected since the last creative epoch), and therefore,
à fortiori, in what I conceive to be its truer meaning ;
there is yet another point on which I would desire to be
interpreted aright, whilst endeavouring to substantiate
the action of local influences on the members of the
insect world. It has been my aim, in the preceding
pages, to call attention to the importance of external
circumstances and conditions in regulating, within defi-
nite limits, the outward aspect of the Articulate tribes.

* Vide supra, p. 128.

ET Ore ae oa

sabia ai e e s ait am

Sc lh sa a A

186

I do not, however, assert that every species is liable to
be interfered with ad extra; that is a question which
the greater or less susceptibility of the several races, as
originally constituted, can alone decide ; still less would
I willingly lend a helping hand to that most mischievous
of dogmas, that they are all-important in their opera-
tion,—or, in other words, that they possess within them-
selves the inherent power (though it may not invariably
be exercised) of shaping out (provided a sufficient time
be granted them, and in conjunction with the advancing
requirements of the creatures themselves) those perma-
nent organic states to which the name of species (in a
true sense) is now applied. Such a doctrine is in reality
nothing more than the transmutation theory, in all its
unvarnished fulness; and I do not see how it can be for
a moment maintained, so long as facts (and not reason-
ing only) are to be the basis of our speculations. I
repeat, that it is merely within fixed specific bounds that
I would advocate a freedom of development, in obedi-
ence to influences from without: only I would widen

those limits to a much greater extent than has been
ordinarily done,—so as to let in the controlling prin-

ciple of physical agents, as a significant adjunct for our
contemplation.

It does indeed appear strange that naturalists, who
have combined great synthetic qualities with a profound
knowledge of mimutiz and detail, should ever have
upheld so monstrous a doctrine as that of the transmis-
sion of one species into another,—a doctrine, however,

187

which arises almost spontaneously,—if we are to assume
that there exists in every race the tendency to an un-
limited progressive improvement. There are certainly
no observations on record which would, in the smallest
degree, countenance such an hypothesis. Many animals
and plants, it is true, are capable of considerable modifi-
cations and changes, for the better,—very much more
than is the case with others. But what does this prove,
except that their capacity for advancement has a slightly
wider compass than that of their allies? It touches not
the fact, that the boundaries of their respective ranges
are absolutely and critically defined. It is moreover a
singular phenomenon, and one in which the strongest
proofs of design (or a primary adjustment of limits with
a view to the future) may be discerned, that the mem-
bers of the organic creation which display the greatest
adaptive powers, are those which were apparently des-
tined to become peculiarly attendant upon man. “ithe
best-authenticated examples,” says Sir Charles Lyell,
“of the extent to which species can be made to vary
may be looked for in the history of domesticated animals
and cultivated plants. It usually happens that those
species which have the greatest pliability of organiza-
tion, those which are most capable of accommodating
themselves to a great variety of new circumstances, are
most serviceable to man. These only can be carried by
him into different climates, and can have their pro-
perties or instincts variously diversified by differences of
nourishment and habits. If the resources of a species

188

be so limited, and its habits and faculties be of such a
confined and local character, that it can only flourish in
a few particular spots, it can rarely be of great utility.
We may consider, therefore, that in the domestication
of animals and the cultivation of plants, mankind have
| first selected those species which have the most flexible
| frames and constitutions, and have then been engaged
| for ages in conducting a series of experiments, with
much patience and at great cost, to ascertain what may
be the greatest possible deviation from a common type
which can be elicited in these extreme cases*,”?

The fact, however, that all areas of aberration (how-
ever large they may be) are positively circumscribed,
need scarcely be appealed to, in exposing the absurdity
of the transmutation hypothesis. The whole theory is
full of inconsistencies from beginning to end; and from
whatever point we view it, it is equally unsound. How,
for instance, can any amount of local influences, or the
progressive requirements of the creatures themselves,
| give rise to the appearance of several well-marked re-

) | presentatives of a. genus on the self-same spot,—where

| the physical conditions for each of them are absolutely
\the same? Look, for example, at the Tarphii (to which
I have already alluded+) of Madeira: I have detected
about eighteen abundantly defined Species; and, as
stated in a previous chapter, I have but little doubt,
from their sedentary habits, and the evident manner in

y * Principles of Geology, 9th edition, pp. 583, 584.
” Uae et Vide supra, p. 121. ;

189

which they are adjusted to the peculiarities of the region
in which they obtain, that they are strictly an esoteric
assemblage, inhabiting the actual sites (or nearly so) of
their original début upon this earth. Here, then, we
have a sufficient length of time for developments to have
taken place; they are all exposed to the self-same
agencies from without (for they live principally in com-
munion) ; yet, though I have examined carefully more
than a thousand specimens (a large proportion of them
beneath the microscope), I have never discovered a
single intermediate link which could be regarded as in a
transition state between any of the remainder. But
how is this ?—Is it possible to account for differences so
decided, yet each of such amazing constancy, amongst
the several creatures of a central type which have been
exposed to identical conditions through, at any rate,
generations innumerable? They clearly cannot be ex-
plained on the doctrine of transmutation : yet they are
no exceptions to the ordinary rule,—occupying an ana-
logous position to the members of every other endemic
group. s

But I will not occupy more space on the transmuta-
tion theory: suffice it to have shown that, in thus con-

ceding a legitimate power of self-adaptation, in accord-
ance with external circumstances, to the members of the
insect world; and in suggesting the inquiry, whether
the action of physical influences has been adequately
allowed for by entomologists generally (or, in other
words, whether the small shades of difference which

190

have often, because permanent, been at once regarded
as specific, may not be sometimes rendered intelligible .
by a knowledge of the localities in which the creatures
have been matured), I do not necessarily open the door
to the disciples of Lamarck, or infringe upon the strict
orthodoxy of our zoological creed. On the contrary,
indeed, I believe that the actual reverse is nearer the
truth; and, moreover, that those very hyper-accurate
definers who recognize a “species” wheresoever the
minutest decrepancy is shadowed forth, will be found
eventually (however unaware of it themselves) to have
been the most determined abettors of that dogma,—see-
ing that their species, if such they be, do most assuredly
pass into each other.

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We must not, however, omit to notice, briefly, how
this perversion of Nature’s economy took its rise. It
was from the desire, which is almost inherent within us,
to account for everything by physical laws; and to dis-
pense with that constant intervention of the direct crea-
tive act which the successive races of animals and plants,
such as are proved by geology to have made their appear-
ance at distinct epochs upon this earth, would seem to
require. Or, which amounts to the same thing, it
resulted through an endeavour to explain by material
processes what is placed beyond their reach. But, if
this be the case, it may be reasonably asked,—Are mate-
rial laws then not to be inquired into, and should the
various influences which operate in the organic world
around us be debarred from analysis? Unquestion-

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191

ably not. Truth is truth, under whatever aspect it may
come; and cannot possibly contradict another truth.
To exercise our intellectual faculties, by tracing out,
through slow, inductive methods, the modus operandi of
even a single natural law, is an honourable task; nor
should the apparent smallness of the media which we
are at times compelled to employ, render it less so (else
would this present treatise, like many others of a kindred
stamp, have been best unwritten) : but it is from the
conceit that our own imperfect interpretations have left
nothing more to be found out, that the great danger is
to be anticipated. An effect may be literally dependent
upon a certain proximate cause ; and if we be so fortu-
nate as to ascertain that cause, we have done something ;
but it does not necessarily follow that we have done much.
On the contrary, it often happens that, in so doing, we
have achieved wonderfully little, —seeing that the pro-
blem may be self-evident. Behind that “cause,” we
should recollect, others lie concealed, of a far deeper
nature, each depending upon the next in succession to
it; until, in the order of causation, we are at length led
back, step by step, to the Final One,—with which alone
the mind can be thoroughly content. “We make dis-

covery after discovery,” says Dr. Whewell, “in the
satisfactory,

various regions of science; each, it may be,
Something

and in itself complete, but none final.
always remains undone. The last question answered,
the answer suggests still another question. The strain

of music from the lyre of Science flows on, rich and

p
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192

sweet, full and harmonious; but never reaches a close:
no cadence is heard with which the intellectual ear can —
feel satisfied *.”

As regards that most obscure of questions, what the
limits of species really are, observation alone can decide
the point. It frequently happens indeed that even
observation itself is insufficient to render the lines of
demarcation intelligible, —therefore, how much more
mere dialectics! To attempt to argue such a subject
on abstract principles, would be simply absurd ; for, as
Lord Bacon has remarked, “the subtilty of Nature far
exceeds the subtilty of reasoning :” but if, by a careful
collation of facts, and the sifting of minute particulars
gathered from without, the problem be fairly and deli-
berately surveyed, the various disturbing elements which
the creatures have been severally exposed to having been
duly taken into account, the boundaries will not often be
difficult to define. Albeit, we must except those races
of animals and plants which, through a long course of
centuries, have become modified by man,—the starting-
points of which will perhaps continue to the last shrouded
in mystery and doubt. It would be scarcely consistent —
indeed to weigh tribes which have been thus unnaturally
tampered with by the same standard of evidence as we
require for those which have remained for ever un-
touched and free,—especially so, since (as we have already
observed) it does absolutely appear, that those species, the
external aspects of which have been thus artificially con-

* Indications of the Creator (London, 1845), p. 163.

trolled, are by constitution more tractile (and possess,
therefore, more decided powers for aberration) than the

rest. Whether traces of design may be recognized in Piyw*™

this circumstance, or whether those forms were originally
selected by man on account of their pliability, it is not
for me to conjecture ; nevertheless, the first of these in-
ferences is the one which I should, myself, be à priori
inclined to subscribe to.

In examining, however, this enigma, of the limits
within which variation is (as such) to be recognized ; it
should never be forgotten, that it is possible for those
boundaries to be absolutely and critically marked out
even where we are not able to discern them: so that the
difficulty which a few domesticated creatures of a singu-
larly flexible organization present, should not unneces-
sarily predispose us to dispute the question in its larger
and more general bearings. Nor should we be unmind-
ful that (as Sir Charles Lyell has aptly suggested) “some
mere varieties present greater differences, inter se, than
do many individuals of distinct species ;” for it is a truth
of considerable importance, and one which may help us
out of many an apparent dilemma.

But, whatever be the several ranges within which the
members of the organic creation are free to vary; we
are positively certain that, unless the definition of a species,
as involving relationship, be more than a delusion or ro-
mance, their circumferences are of necessity real, and
must be indicated somewhere,—as strictly, moreover, and
rigidly, as it is possible for anything in Nature to he

—
— =

a ae i A “5

See

nasi ee

194

chalked out. The whole problem, in that case, does in
effect resolve itself to this——Where, and how, are the
lines of demarcation to be drawn? No amount of incon-
stancy, provided its limits be fixed, is irreconcilable with
the doctrine of specific similitudes. Like the ever-
shiftmg curves which the white foam of the untiring
tide describes upon the shore, races may ebb and flow;

but they have their boundaries, in either direction,
beyond which they can never pass. And thus in every
species we may detect, to a greater or less extent, the
emblem of instability and permanence combined: al-
though perceived, when inquired into, to be fickle and
fluctuating in their component parts, in their general
outline they remain steadfast and unaltered, as of old,—

“ Still changing, yet unchanged; still doom’d to feel
Endless mutation, in perpetual rest.”

———e

Aberration, perhaps indicated universally, 16, 17, 18.

Aborigines, insect, unimportant for climatal modifications, 25, 20 2).

Acalles, the Canarian type of, apparent on the Salvages and De-

zertas, 124.

Neptunus, Woll., perhaps a state of A. argillosus, 124.
Achatina Eulima, Lowe, its extinction in Porto Santo, 131.
Achenium Hartungii, Heer, a form of A. depressum, 65.

Acherontia Atropos, Linn., its introduction into Madeira perhaps

recent, 74.

Adimonia, the capture of, out at sea, 150.

Aépus marinus, Ström., pallid hue of, 64.

Robinii, Lab., pallid hue of, 64.

Agabus bipustulatus, Linn., unaffected by climate, 31.

Alligators, their peculiarity to S. America, 143.

Alpine species, some peculiarly so, 40.

Altitude and latitude, sometimes reciprocal, 35, 114.

Amycterus, its concentration in Australia, 143.

Amyot, M., his ‘ Méthode Mononomique,’ 164.

Analogies, Lord Bacon on the importance of, 13; why necessary to

be studied, 14.

Analogy, argument from, 10, 11, 12.

Anchomenus marginatus, Linn., slightly modified in Madeira, 38.

Andes, dissimilarity of the fauna on the opposite sides of the, 146.

Anobium striatum, Oliv., unaffected by climate, 3l.

Antennæ, joints of, said occasionally to vary, 96.

Anthicus bimaculatus, Iig., variability of, near the sea, 63.
fenestratus, Schmidt, slightly modified in Madeira, 38.
humilis, Germ., variability of, in salt places,

—— instabilis, Hoffm., pallid hue of, 64.

Anthonomus ater, Mshm, very small in Lundy Island, 58, 73.

Aphelocheirus estwalis, Fabr., the hemelytra of, sometimes fully

developed, 100.
Aphodius nitidulus, Fabr., paler in Madeira than in Europe gene-

rally, 65.
K2

196 INDEX.

Aphodius plagiatus, Linn., usually black in England, 61; two
distinct states of, indicated, 105.

Apocyrtus, its concentration in the Philippine Islands, 143.

Apotomus, common to Madeira and Sicily, 139.

Argutor, always apterous in Madeira, 82; trophi of, almost iden-
tical with those of Calathus, 175.

Armadillos, their peculiarity to 8. America, 143.

Armitage, Mr., on Cicindela fasciatopunctatafrom Mount Olympus,41.

Arrangement, a lineal one is not indicated in Nature, 163.

Atlantic continent, Prof. E. Forbes on the former existence of, 137.

Atlantis of the ancients, the impossibility of its being identified
with a former Atlantic region, 140; perhaps the New World, 141.

Atlantis, the genus, a modification of Laparocerus, 143.

Azores, the colonization of, by two Madeiran Helices, 133.

Bacon, Lord, on the importance of analogies, 13; on the Atlantis
of the ancients, 141; on the necessity of observation for forming
science, 159.

Banksias, their concentration in Australia, 142.

Barriers, natural, the difference between primary and recent, 145 ;
their hindrance to insect diffusion, 145.

Bembidium Atlanticum, Woll., paler in Porto Santo than in Ma-
deira, 66; the variations to which it is subject, 107, 108.

bistriatum, Dufts., paler in saline districts, 62.
ephippium, Mshm, pallid hue of, 64.
—-— obtusum, Sturm, varies in southern latitudes, 33.
pallidipenne, Illig., pallid hue of, 64.
sawatile, Gyll., variety of, on the south coast of England, 60.
—— Schmidtii, Woll., perhaps a state of B. callosum, 66.
—— scutellare, Germ., pallid hue of, 64.
tabellatum, Woll., perhaps a state of B. tibiale, 66.

Berginus, common to Madeira and Sicily, 139.

Black Rat, nearly exterminated in England, 178.

Blemus areolatus, Creutz., paler in brackish places, 62.

Bolitochara assimilis, Kby, smallness of, in the Scilly Islands, 73.

Boromorphus, common to Madeira and Sicily, 139.

Brachinus crepitans, Linn., two distinct sizes of, frequently indi-
eated, 105.

Bradycellus fulvus, Mshm, apterous in Madeira, 85.

Bread-fruit Trees, their peculiarity to the South Sea Islands, 142.

Calathus, apterous in Madeira, 82; its trophi almost identical with
those of Pristonychus, 175.
complanatus, Koll., varies from altitude, 39; variety of, on one
of the Madeira Islands, 88.
—— fuscus, Fabr., slightly modified in Madeira, 38, 85.

INDEX. 197

melanocephalus, Linn., smallness of, in the Scilly Islands,

mollis, Mshm, variable in its wings, 43 ; lurid colour of, 64.

Calcareous soils, effect of, on the aspect of insects, 66.

Calceolarias, their concentration on the Andes, 142.

Calosoma, a species of, ten miles from shore, 147 ; the genus, merges
gradually into Carabus, 175.

Syncophanta, Linn., its power of crossing the sea, 147.
Canary Islands, migratory direction of their insect population, Lids
Carabide, inconstant in their organs of flight, 43 ; family of, nearly

similar throughout in its oral organs, 174.
Carpophilus hemipterus, Linn., unaffected by climate, 31.
Caulotrupis conicollis, Woll., large size of, on one of the Madeira
Islands, 88, 109.
lucifugus, Woll., varies from isolation, 90, 109..
Causes, never final ones which we investigate, 191.
Centrinus, its concentration in S. America, 143.
Ceutorhynchus contractus, Mshm, smallness of, in Lundy Island,
59, 73. ;
Cholovocera, common to Madeira and Sicily, 139.
Choreius ineptus, Westw., on a winged state of, 44.
Chorosoma miriforme, the development of the wings of, 100.
Chrysomela, apterous in Madeira, 82.
Chrysomele, vary from altitude, 41.
Chrysomelide, almost absent in Tierra del Fuego, 47.
Cicindela fasciatopunctata, Germ., a state of C. sylvatica, 4l.
Cicindelide, often variable, a
Cillenum laterale, Sam., lurid hue of, 64.
Cimex apterus, Linn., the development of the wings of, 100.
__— lectularius, Linn., on the development of the wings of, 45.
Cistela sulphurea, Linn., its variability near the sea, 60.
Clausilia deltostoma, Lowe, a Porto-Santan form of, 134.
Climatal modifications significant, although small, 42.
Climate, not important as a disturbing cause, 23, 24, 31, 32, 42.
Clouded-yellow Butterfly, unaffected by climate, 31.
Clypeaster pusillus, Gyll., differs slightly in Madeira, 65.
Coast, inconstancy of insects in the vicinity of the, 57.
Coccinella 7-punctata, Linn., unaffected by climate, 3l.
Colias Edusa, Fabr., unaffected by climate, 31.
Colour, its inconstancy in insects found near the sea, 57, 58.

of insects, affected by isolation, 88.

Colymbetes, a species of, captured forty-five miles from shore, 149,150.

Compensation, generally apparent when an insect is deprived of an
organ or sense,

Coranus subapterus, Curt., the development of the wings of, 101.

Cordillera, Mr. Darwin on the fauna of the, 145.

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198 INDEX.

Corylophus, apterous in Madeira, 82.

Criomorphus, Curtis, referable to the genus Delphazx, 45.
Cyclostoma lucidum, Lowe, its extinction in Porto Santo, 13].
Cynthia Cardui, Linn., unaffected by climate, 32.

Cynucus, a species of, seventeen miles from shore, 150.
Cyrtonota, its concentration in S. America, 143.

Darwin, Mr., on the fauna of the Galapagos, 23; relative propor-
tions of the insect tribes in the tropics, 28, 29; on the insects of
Tierra del Fuego, 47 ; on the natural features of Tierra del Fuego,
50; on the insects of Keeling Island, 55; on the insects of St.
Helena, 55; on the insects of Ascension, 55; on the apterous
condition of insular species, 86; on the fauna of the Cordillera,
145; on a Calosoma captured at sea, 147; on insects captured
in the sea, 149, 150; on the disappearance of animals before
more powerful ones than themselves, 178.

Dawson, Rev. J. F., on a variety of Bembidium sazxatile, 60.

Definition of the term ‘ species,’ 4; of the term ‘ variety,’ 4.

Delphax, on the development of the wings of, 45.

Dermestes vulpinus, Fabr., unaffected by climate, 31.

Deucalion, its occurrence on the Salvages and Dezertas, 125.

Desertarum, Woll., its sedentary nature, 125, 126, 127.

Dichelus, its concentration in S. Africa, 143.

Differences, when to be regarded as specific, 6; too exclusively
studied, 12.

Diffusion, various means of, which operate on the insect tribes, 148.

Disturbing agents, Prof. Henfrey on, 8.

Ditylus, the same type of, indicated in the Canaries and Salvages, 124.

Domesticated animals, pliable nature of, 187, 192.

Dromius arenicola, Woll., representative of D. obscuroguttatus, 66.

fasciatus, Gyll., its paleness near the sea, 63.

negrita, Woll., perhaps an ultimate state of D. glabratus, 85.

obscuroguttatus, Dufts., its changes in Madeira, 36, 37, 38;
apterous in Madeira, 84.

sigma, Rossi, its colour affected by isolation, 88, 89.

Elevation, sometimes corresponds with latitude, 35, 114.

Ellipsodes glabratus, Fabr., singular variety of, on one of the Ma-
deira Islands, 88, 109.

Elytra, connateness of, a variable character, 96.

‘Endemic,’ to what species the term is applicable, 118.

Entomology, the study of, does not necessarily cramp the mind, 111.

Ephistemus, apterous in Madeira, 82.

Eucalypti, their concentration in Australia, 142.

Eunectes sticticus, Linn., unaffected by climate, 31. -

Euphorbias, their concentration in Southern Africa, 142.

INDEX. 199

Eurygnathus Latreillei, Lap., variety of, on one of the Madeira
Islands, 88, 109.

Exceptions, not be allowed to negative a law, 72, 73.

Extinction of species, as indicated in the Madeiran Helices, 131 ;
the only cause by which genera may be abruptly defined, 176.

Forbes, Prof. E., on the origin of the British animals and plants,
130; his epochs of migration of the British animals and plants,
136; on the existence of a former Atlantic continent, 137.

Forests, the hindrance which they offer to insect-diffusion, 154.

n reari Islands ” of the ancients, probably the Canarian group,

Galapagos, fauna of, 23.

Genera, the nature of, often misunderstood, 160; a familiar expla-
nation of, 160, 161, 162; cannot be abrupt except trom accident,
169; how to be defined, 169; the types of, usually situated
towards the centres of the several groups, 170; the types of,
usually evenly balanced in their structural characters, 171, 172;
may be abruptly defined from accidental causes, 176, Mids

Generic areas, an important feature throughout Nature, 130, 141, 184.

Geology, a necessary item in the study of insect-diffusion, 113.

Germanic plains, the, probably a primary area of diffusion, 130.

Gerris, on the development of the wings of, 100.

Gould, Mr., on the Swallows of Malta, 102.

Gymnaétron, blood-red dashes characteristic of, 62.

Campanule, Linn., its smallness on the Cornish coast, 58.

—— Veronice, Germ., a variety of G. niger, 62.

Hadrus illotus, Woll., perhaps a form of H. cinerascens, 66.
Haliplus obliquus, Gyll., dark state of, in Ireland, 67.
Haltica exoleta, Fabr., its variability on the coast, 59.
Harcourt, Mr., on the discovery of Madeira, 49, 50.
Harpalus vividus, Dej., changes to which it is subject, 67, 68, 69;
variable in the connateness of its elytra, 96, 97.
Hegeter, its maximum attained in the Canaries, 120.
elongatus, Oliv., its migration from the Canaries, 120; of a
more adaptive nature than its allies, 12h,
latebricola, Woll., its occurrence in the Salvages, 120.
Helices, have often two distinct states, 106; many of them repre-
sentative in the Madeira Islands, 128, 129 ; those in the Madeiras
chiefly of slow migratory powers, 130, 131.
Helix attrita, Lowe, its local character, 132.
Eo ~ Fér., perhaps a gigantic state of H. punctulata,
106.
—— calculus, Lowe, sedentary nature of, 132.

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200 INDEX.

Helix commigta, Lowe, sedentary nature of, 132.
coronata, Desh., its peculiarity to Porto Santo, 128; its occur-
rence beneath the surface of the ground, 131.
coronula, Lowe, its peculiarity to the Southern Dezerta, 128.
Delphinula, Lowe, the Madeiran representative of H. tectifor-
mis in Porto Santo, 129.
discina, Lowe, a form of H. polymorpha, 133.
erubescens, Lowe, its powers of diffusion greater than those of
its allies, 133; sensitive to external influences, 134.
Jluctuosa, Lowe, its extinction in Porto Santo, 131.
hirsuta, Say, two distinct states of, 106.
—— lapicida, Linn., its extinction in Porto Santo, 131.
latens, Lowe, the Madeiran representative of H. obtecta in
Porto Santo, 129.
—— lincta, Lowe, the common Madeiran form of H. polymorpha,
134.
—— Lowei, Pfr., perhaps a gigantic state of H. Portosanctana, 106.
—— papilio, Lowe, a form of H. polymorpha, 133.
paupercula, Lowe, its powers of diffusion greater than those
of its allies, 133.
polymorpha, Lowe, sensitive to external influences, and of
great diffusive powers, 133.
Portosanctana, Sow., its peculiarity to Porto Santo, 129.
pulvinata, Lowe, a form of H. polymorpha, 133.
saccharata, Lowe, a local state of H. polymorpha, 134.
senilis, Lowe, the Dezertan form of H. polymorpha, 134.
squalida, Lowe, the Madeiran representative of H. depauperata
in Porto Santo, 129.
—— tiarella, Webb, its sedentary nature, 128.
undata, Lowe, its peculiarity to Madeira proper, 129.
—— Vulcania, Lowe, its peculiarity to the Dezertas, 129.
Wollastoni, Lowe, sedentary nature of, 132.
Helobia nivalis, Payk., perhaps a state of H. brevicollis, 40.
Helops, always apterous in Madeira, 82. _
confertus, Woll., varies from altitude, 39.
—— futilis, Woll., varies from isolation, 109.
~— testaceus, Küst., pallid hue of, 64.
—— Vulcanus, Woll., large size of, on one of the Madeira Islands, 88.
Henfrey, Prof., on disturbing agents, 8.
Herschel, Sir John, on the requisites for an observer, 12,
Hipparchia Semele, Linn., has a distinct aspect in Madeira, 34.
Hipporhinus, its concentration in S. Africa, 143.
Holme, Mr., on Olisthopus rotundatus in the Scilly Islands, 58, 102 ;
on a winged state of Phosphuga atrata, 102.
Holoparamecus, common to Madeira and Sicily, 139.
niger, Aubé, different in Madeira and Sicily, 33.

INDEX. 201

Hooker, Dr., on the insects of Kerguelen’s Land, 86.
Humboldt, his notice of Sphinxes and flies high up on the Andes, 149.
a their peculiarity to S. America and the W. Indies,

444.
Hydrobius, apterous in Madeira, 82; the capture of, out at sea, 150.
Hydrometride, on the development of the wings of, 100.
Hydroporus, the capture of, out at sea, 150.

confluens, Fabr., unaffected by climate, 3l.

Hypsonotus, its concentration in 5. America, 143.

Influence of climate not important, 23.

Insect-aberration, perhaps a universal fact, 16, 17, 18.

Insule Fortunate of Juba, probably the Canarian Group, 141.

Ireland, poverty of the fauna of, 52, 535 the south-west of, has
something in common with Madeira, 139.

Islands, faunas of, often too greatly magnified, 70; the species of,
eel more isolated in their structure than those of continents,

Isolation, effects of, on insect-stature, 71.

Ixias, their concentration im Southern Africa, 142.

Kangaroos, their concentration in Australia, 142.
Kerguelen’s Land, imsects of, 86.

Kirby, Rev. W., on insects washed up on the Suffolk coast, 147.

Lemophleus pusillus, Schdnh., unaffected by climate, 31.

Lamprias chlorocephalus, Ent. H., two distinct sizes of, frequently
indicated, 105.

Laparocerus morio, Schouh., large size of, on one of the Madeira
Islands, 88.

Latitude and altitude, sometimes reciprocal, 35.

Leistus montanus, Steph., has been supposed to be equal to L. fulvi-
barbis, 40.

Lemur, its peculiarity to Madagascar, 143.

Litargus, common to Madeira and Sicily, 139.

Ligus angustatus, Fabr., unaffected by climate, 31.

Localities, some naturally more productive than others, 53, 54.

Longitarsus, the native species of, apterous in Madeira, 82.

Loricera, apterous in Madeira, 82.

Lowe, Rev. R. T., his capture of Deucalion Desertarum, 127.

Lundy Island, smallness of the insects in, 58, 59; occurrence of the
Black Rat in, 178.

Lycena Phieas, Linn., darker in Madeira than in England, 34.

Lyell, Sir Charles, on Helix hirsuta, 106; on the fossil period of
the Madeiran Helices, 129; on insects washed up on the shore,
148; on the effect of gales in the transportation of insects, 148 ;

202 INDEX.

on the effects of a volcanic eruption in destroying species, 179; on
the flexible nature of certain animals and plants, 187; on the greater
differences which varieties often present than do species, 193.

Lygeus brevipennis, Latr., on the development of the wings of,
101.

Macronota, its peculiarity to Java, 143.

Madeira, has some features in common with Tierra del Fuego, 48,
49,50, 51; former state of, 48, 49; great fire on the southern
side of, 49; origin of the name of, 50; the insects of, 55; the
tendency of its insects to become apterous, 82; the migratory
direction of its insect population, 119; the local nature of its
various species, 152, 153.

Magnolias, their concentration in Central America, 142.

Malta, Mr. Gould on the birds of, 102.

Malthodes Kiesenwetteri, Woll., perhaps a state of M. brevicollis, 66.

Man, agency of, in the destruction of species, 179.

Mantura Chrysanthemi, Ent. H., variability of, ia Lundy Island, 59.

Marsupialia, their concentration in Australia, 142.

Mesembryanthemums, their concentration in Southern Africa, 142.

Mesites, a modification of Cossonus, 144.

Maderensis, Woll., its near relationship to the M. Tardii, 141.
Tardii, Curtis, its variability near the coast, 58.
‘Méthode Mononomique,’ the unsoundness of, 164—168.
Migratory powers, slowness of, in the Madeiran Helices, 130—132.
progress, direction of, in the Madeiran animals, 120, 135.

Mimosas, their concentration in Australia, 142.

Mollusca, Terrestrial, often present two distinct states, 106.

Moluris, its concentration in S. Africa, 143.

Monochelus, its concentration in S. Africa, 143.

Mountain-chains, their hindrance to insect-diffusion, 145.

Mountain-tops, either very prolific in insect life, or else barren, 115.

Mus Rattus, almost exterminated in England, 178.

Mycetoporus pronus, Erichs., two distinct states of, indicated, 106.

Myrtles, their concentration in Australia, 142.

Naturalist, the, what his province to investigate, 158.

Nature, not irregular because presenting occasional anomalies, 94.

Naupactus, its concentration in S. America, 143.

Nebria complanata, Linn., unusually pale near Bordeaux, 33 ; pallid
hue of, 64.

New World, some of its insects perhaps but states of those of the
Old, 37.

Nomenclature, a binomial system the only true one, 164, 168.

Notuphus, the capture of, out at sea, 150.

Notiophili, extremely variable, 40.

INDEX. 2038

Notiophilus geminatus, Dej., large size of, on one of the Madeira
Islands, 88.

Observation, indispensable in natural science, 20, 159, 192.

Ocean, the, its hindrance to insect-diffusion, 145.

Ochthebius marinus, Payk., lurid hue of, 64.

Olisthopus, apterous in Madeira, 82.
> _ a Woll., large state of, on one of the Madeira Islands,

rotundatus, Payk., very small in the Scilly Islands, 58, 793

subapterous in the Scilly Islands, 102.

Omaseus nigerrimus, Dej., a form of O. aterrimus, 33.

Omias Waterhousei, Woll., large state of, on one of the Madeira
Islands, 88, 109.

Oncocephalus griseus, development of the wings of, 101.

Othius, apterous in Madeira, 82. ;

Ourangs, their peculiarity to the Indian Islands, 143.

Oxyomus, a modification of Aphodius, 144.

Pachymerus brevipennis, the development of the wings of, 100.
Pachyrhynchus, its concentration in the Philippine Islands, 143.
Painted-Lady Butterfly, unaffected by climate, 32,

Papilio Machaon, Linn., unaffected by climate, 31.

Paropsis, its concentration in Australia, 143.

Patagonia, insects of, distinct from those of Tierra del Fuego, 47, 48.

Patrobus septentrionis, Dej. has been supposed to be a state of P.
excavatus, 40.

Pecteropus, its maximum attained in the Canaries, 124.

Maderensis, Woll., varies from altitude, 39.
rostratus, Woll., varies from isolation, 90.

Pelargoniums, their concentration in Southern Africa, 142.

Pelophila borealis, Payk., larger in Ireland than in the Orkneys, 33.

Phaleria cadaverina, Fabr., pallid hue of, 64.

Philhydrus melanocephalus, Oliv., two states of, frequently indicated,
105.

Phiwophagus, apterous in Madeira, 82.

Phosphuga atrata, Linn., taken with the wings developed, 102.

subrotundata, Leach, the Irish form of the P. atrata, 33.

Phytophaga, preponderance of, in the tropics, 28, 29.

Pieris Brassica, Linn., varies in Nepaul and Japan, 34.

Pissodes notatus, Fabr., unaffected by climate, 30.

Platyomus, its concentration in S. America, 143.

Platyrrhini, their peculiarity to $. America, 14

Pogonus luridipennis, Germ., lurid hue of, 64.

Pontia Brassice, Linn., its introduction into Madeira probably re-
cent, 74-

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204: INDEX.

Porto Santo, origin of the name of, 49; a generic area of radiation
for certain Helices, 130. ;
Predacious insects, less numerous in the tropics; 28, 29.
Prostemma guttula, Fabr., the development of the wings of, 100, 101.
Psylliodes, a variable species of, in Lundy Island, 60.
erythrocephala, Linn., two distinct states of, frequently indi-
cated, 105.
marcida, Tig., pallid hue of, 64.
nigricollis, Mshm, a pale state of the P. erythrocephala, 105.
vehemens, Woll., varies from isolation, 90.
Pterostichus, its various divisions are natural ones, 175.
Ptini, their stature affected by isolation, 74; which characters of,
are the most constant, 104.
Ptinus albopictus, Woll., its changes on the islands of the Madeiran
Group, 75—77.
Pupa, often two distinct states of, 106.
Purpurarie of the ancients, probably the Madeiran Group, 141.
Pyrenean region, the, perhaps a primary area of diffusion, 130.

Reasoning, not sufficient of itself for the formation of science, 159.

Red-Admiral Butterfly, its introduction into Madeira perhaps re-
cent, 74.

Reduviade, on the development of the wings of a representative of
the, 101.

Representative species, exemplified by the Madeiran Helices, 128,
129, 185; where frequently to be recognized, 183.

Rhyzopertha pusilla, Fabr., unaffected by climate, 31.

Rivers, their power of transporting insects along their course, 149.

Saline spots, variation of insects in, 57.
Salvages, occurrence of a Canarian form on the, 120, 124.
Saprinus, a modification of Hister proper, 143.
nitidulus, Fabr., two distinct states of, indicated, 106.

Scarabeus, the capture of, out at sea, 150.
Scarites abbreviatus, Koll., large size of, on one of the Madeira

Islands, 88; varies both from isolation and altitude, 91,
Sciences, the, should assist rather than oppose each other, 155, 156.
Scydmenus Helfert, Schaum, smaller in Madeira than in Sicily, 65.
Scymnus, an apterous species of, in Porto Santo, 82.
Sea, inconstancy of insects in the vicinity of the, 57.
Sicily, the fauna of, has much in common with that of Madeira, 139.
Silpha atrata, Linn., presents a distinct state in Ireland, 33.
Silybum Marianum, Grtn., its stalks the food of a Ptinus, 76.
Similitudes, Lord Bacon on the importance of, 13.
Sttonia gressoria, Illig., perhaps a form of the S. grisea, 33.
Sitophilus granarius, Linn., unaffected by climate, 31.

INDEX. 806

Sitophilus oryze, Linn., unaffected by climate, 31.

Sloths, their peculiarity to S. America, 143.

Species, definition of the term, 4; familiar explanation concerning
the nature of, 161, 162; limitation of, how to be attempted, 192 ;
limits of, real, though often difficult to trace out, 193; in a cer-
tain sense both unstable and permanent, 194.

Specific centres of creation, 5.

Sphinx Convolvuli, Linn., its introduction into Madeira probably
recent, 74.

e i on one of the Reduviade, 101; on Oncocephalus griseus,

Stapelias, their concentration in Southern Africa, 142.

States, large and small ones indicated in some insects, 105.

Stature of insects, smaller in islands than on continents, 70.

Stenolophus Skrimshiranus, Steph., perhaps a state of S. Teutonus,

Stenus Heeri, Woll., two distinct states of, indicated, 106.
Structural characters, seldom variable in the Insecta, 95.
Subsidences, the effect of, on insect life, 114.
Swallow-Tail Butterfly, unaffected by climate, Se
Syncalypta, apterous in Madeira, 82.

Tachyporus nitidicollis, Steph., perhaps a state of T. obtusus, 33.

Tarphii, their economy m the Madeira Group, 121.
Tarphius, its maximum attained in Madeira proper, 121; common
to Madeira and Sicily, 139.
gibbulus, Germ., the Sicilian exponent of the genus, 123.
Lowei, Woll., of a more adaptive nature than its allies, 122.
Tarus, always apterous in Madeira, 82.
lineatus, Schonh., assumes a distinct state in Madeira, 65.
Telephorus testaceus, Linn., its variability in Lundy Island, 59.
Thompson, Mr., on the reptiles of Ireland, England, and Belgium,
136.
Thorictus, common to Madeira and Sicily, 139.
Tierra del Fuego, insects of, 47; has many characters in common
with Madeira, 48—51. .
Time, an important item in the question of modifications, if
Toucans, their peculiarity to S. America and the W. Indies, .
Transmutation-theory, unsoundness of the, 186—189 ; how it took
its rise, 190.
Trechus, always apterous in Madeira, 82.
alticola, Woll., perhaps a state of T. custos, 39.
lapidosus, Daws., pallid hue of, 64.
Tree-Porcupines, their peculiarity to S$. America, 143.
Tribolium ferrugineum, Fabr., unaffected by climate, Ər
Trogosita mauritanica, Linn., unaffected by climate, 3T.

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206 INDEX.

Tropics, exuberance of the, 27,28; relative proportions of the insect
tribes within the, 28, 29.
Tychius, always apterous in Madeira, 82.

Unity, indicated in the organic creation, 179, 180.

Vanessa Atalanta, Linn., has a different aspect in N. America, 34;

perhaps a recent introduction into Madeira, 74.
Callirhoé, Fabr., smaller in Porto Santo than in Madeira, 73.

Variation in the Insecta, a matter of experience, 7, 8, 15; probable
from analogy, 15; perhaps indicated in every individual, 16, 17,
18; restricted, 35.

Variety, definition of the term, 4.

Velia, on the development of the wings of, 100.

Waterhouse, Mr., his opinion concerning generic types, 172.

Westwood, Mr., on Papilio Machaon from the Himalayas, 32; on
American specimens of Lycena Phileas, 34; on the effect of heat
in developing the wings of insects, 44; on a winged state of
Choreius ineptus, 44; on the development of the wings in Del-
phax, 45; on a winged state of Cimex lectularius, 45 ; on Aphelo-
cheirus estivalis, 100; on the development of the wings of the
Hydrometride, 100; on Cimex apterus, 100; on Prostemma gut-
tula and Coranus subapterus, 101; on the development of the
wings of Lygeus brevipennis, 101.

Whewell, Dr., on the natural causes which science has to investi-
gate, 191.

White-Cabbage Butterfly, varies in Nepaul and Japan, 34.

Winds, the effects of, in the diffusion of insects, 148.

Wings of insects, subject to undue development in hot seasons, 43 ;
liable to become gradually obsolete in islands, 81; more variable
than other organs, 97.

Xenostrongylus, its geographical distribution, 124; common to
Madeira and Sicily, 139.

Zargus pellucidus, Woll., variety of, on one of the Madeira Islands,
88.

FINIS.

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Lately published, by the same Author,

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INSECTA MADERENSIA ;

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THE MADEIRAN GROUP.

London: Joun VAN Voorst, l, Paternoster Row.

AR dM ain tt ict a e o Ba Ta At hi te BS aa alin,

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Full text of "On the variation of species"

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